Bonding methods for light emitting diodes

ABSTRACT

Disclosed herein are techniques for bonding LED components. According to certain embodiments, a first component including a semiconductor layer stack is hybrid bonded to a second component including a substrate that has a different thermal expansion coefficient than the semiconductor layer stack. The semiconductor layer stack includes an n-side semiconductor layer, an active light emitting layer, and a p-side semiconductor layer. The first component and the second component further include first contacts and second contacts, respectively. To hybrid bond the two components, the first contacts are aligned with the second contacts. Then dielectric bonding is performed to bond respective dielectric materials of both components. The dielectric bonding is followed by metal bonding of the contacts, using annealing. To compensate run-out between the first contacts and the second contacts, aspects of the present disclosure relate to changing a curvature of the first component and/or the second component during the annealing stage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. Non-Provisional applicationSer. No. 16/863,579, filed Apr. 30, 2020, which claims the benefit andpriority under 35 U.S.C. § 119 to U.S. Provisional Patent ApplicationNo. 62/844,558, filed on May 7, 2019, the contents of which are herebyincorporated by reference in their entirety for all purposes.

BACKGROUND

Light emitting diodes (LEDs) convert electrical energy into opticalenergy, and offer many benefits over other light sources, such asreduced size, improved durability, and increased efficiency. LEDs can beused as light sources in many display systems, such as televisions,computer monitors, laptop computers, tablets, smartphones, projectionsystems, and wearable electronic devices. Micro-LEDs (“μLEDs”) based onIII-nitride semiconductors, such as alloys of AlN, GaN, InN, and thelike, have begun to be developed for various display applications due totheir small size (e.g., with a linear dimension less than 100 μm, lessthan 50 μm, less than 10 μm, or less than 5 μm), high packing density(and hence higher resolution), and high brightness. For example,micro-LEDs that emit light of different colors (e.g., red, green, andblue) can be used to form the sub-pixels of a display system, such as atelevision or a near-eye display system.

SUMMARY

This disclosure relates generally to LEDs. More specifically, thisdisclosure relates to methods of bonding components of LEDs, and devicesthat are formed by the bonding methods. According to some embodiments, adevice includes a first component having a semiconductor layer stackincluding an n-side semiconductor layer, an active light emitting layer,and a p-side semiconductor layer. A plurality of mesa shapes are formedwithin the n-side semiconductor layer, the active light emitting layer,and the p-side semiconductor layer. The semiconductor layer stackcomprises a III-V semiconductor material. The device also includes asecond component having a passive or an active matrix integrated circuitwithin a Si layer. A first dielectric material of the first component isbonded to a second dielectric material of the second component, firstcontacts of the first component are aligned with and bonded to secondcontacts of the second component, and a run-out between the firstcontacts and the second contacts is less than 200 nm.

The device may also include a plurality of first trenches that areformed through the semiconductor layer stack between adjacent mesashapes of the plurality of mesa shapes. The device may also include aplurality of second trenches that are formed through at least part of asubstrate on which the semiconductor layer stack is formed. Theplurality of second trenches may be at least partially aligned with theplurality of first trenches.

The device may also include a plurality of first trenches that areformed through the semiconductor layer stack between groups of theplurality of mesa shapes. The device may also include a plurality ofsecond trenches that are formed through at least part of a substrate onwhich the semiconductor layer stack is formed. The plurality of secondtrenches may be at least partially aligned with the plurality of firsttrenches.

The device may also include a thermal expansion coefficient compensationlayer that is formed on a surface of the first component opposite to abonding surface of the first component. The device may also include athermal expansion coefficient compensation layer that is formed on asurface of the second component opposite to a bonding surface of thesecond component.

The first contacts of the first component may have a dished shape. Thesecond contacts of the second component may have a dished shape.

According to some embodiments, a method includes aligning a firstcomponent with a second component by aligning first contacts of thefirst component with second contacts of the second component. The firstcomponent includes a semiconductor layer stack having an n-sidesemiconductor layer, an active light emitting layer, and a p-sidesemiconductor layer. The method also includes performing hybrid bondingof the first component to the second component by performing dielectricbonding of a first dielectric material of the first component with asecond dielectric material of the second component at a firsttemperature, and subsequently performing metal bonding of the firstcontacts of the first component with the second contacts of the secondcomponent by annealing the first contacts and the second contacts at asecond temperature. The second temperature is higher than the firsttemperature. The method also includes compensating a run-out between thefirst contacts and the second contacts. The second temperature may bebetween 150° C. and 250° C.

The method may also include forming a plurality of mesa shapes withinthe n-side semiconductor layer, the active light emitting layer, and thep-side semiconductor layer. Compensating the run-out between the firstcontacts and the second contacts may include forming a plurality offirst trenches through the semiconductor layer stack between adjacentmesa shapes of the plurality of mesa shapes. Compensating the run-outbetween the first contacts and the second contacts may also includeforming a plurality of second trenches through at least part of asubstrate on which the semiconductor layer stack is formed, wherein theplurality of second trenches are at least partially aligned with theplurality of first trenches.

The method may also include forming a plurality of mesa shapes withinthe n-side semiconductor layer, the active light emitting layer, and thep-side semiconductor layer. Compensating the run-out between the firstcontacts and the second contacts may include forming a plurality offirst trenches through the semiconductor layer stack between groups ofthe plurality of mesa shapes. Compensating the run-out between the firstcontacts and the second contacts may also include forming a plurality ofsecond trenches through at least part of a substrate on which thesemiconductor layer stack is formed, wherein the plurality of secondtrenches are at least partially aligned with the plurality of firsttrenches.

Compensating the run-out between the first contacts and the secondcontacts may include forming a thermal expansion coefficientcompensation layer on a surface of the first component opposite to abonding surface of the first component before performing the hybridbonding of the first component to the second component. Compensating therun-out between the first contacts and the second contacts may includeforming a thermal expansion coefficient compensation layer on a surfaceof the second component opposite to a bonding surface of the secondcomponent before performing the hybrid bonding of the first component tothe second component.

Compensating the run-out between the first contacts and the secondcontacts may include forming the first component and the secondcomponent into a concave shape after performing the dielectric bondingand before performing the metal bonding. Compensating the run-outbetween the first contacts and the second contacts may includeperforming dishing of the first contacts of the first component.Compensating the run-out between the first contacts and the secondcontacts may include performing dishing of the second contacts of thesecond component. Compensating the run-out between the first contactsand the second contacts may include performing dishing of the secondcomponent.

This summary is neither intended to identify key or essential featuresof the claimed subject matter, nor is it intended to be used inisolation to determine the scope of the claimed subject matter. Thesubject matter should be understood by reference to appropriate portionsof the entire specification of this disclosure, any or all drawings, andeach claim. The foregoing, together with other features and examples,will be described in more detail below in the following specification,claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments are described in detail below with reference tothe following figures.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment including a near-eye display according tocertain embodiments.

FIG. 2 is a perspective view of an example of a near-eye display in theform of a head-mounted display (HMD) device for implementing some of theexamples disclosed herein.

FIG. 3 is a perspective view of an example of a near-eye display in theform of a pair of glasses for implementing some of the examplesdisclosed herein.

FIG. 4 illustrates an example of an optical see-through augmentedreality system including a waveguide display according to certainembodiments.

FIG. 5A illustrates an example of a near-eye display device including awaveguide display according to certain embodiments.

FIG. 5B illustrates an example of a near-eye display device including awaveguide display according to certain embodiments.

FIG. 6 illustrates an example of an image source assembly in anaugmented reality system according to certain embodiments.

FIG. 7A illustrates an example of a light emitting diode (LED) having avertical mesa structure according to certain embodiments.

FIG. 7B is a cross-sectional view of an example of an LED having aparabolic mesa structure according to certain embodiments.

FIG. 8A illustrates an example of a method of die-to-wafer bonding forarrays of LEDs according to certain embodiments.

FIG. 8B illustrates an example of a method of wafer-to-wafer bonding forarrays of LEDs according to certain embodiments.

FIGS. 9A-9D illustrate an example of a method of hybrid bonding forarrays of LEDs according to certain embodiments.

FIG. 10 illustrates an example of an LED array with secondary opticalcomponents fabricated thereon according to certain embodiments.

FIG. 11A illustrates an example of an LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may have LEDs with vertical and parabolic mesa shapes.

FIG. 11B illustrates an example of another LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may have LEDs with vertical and conical mesa shapes.

FIG. 12A illustrates an example of another LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may undergo n-side processing.

FIG. 12B illustrates an example of another LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may undergo n-side processing.

FIG. 13A illustrates an example of another LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may include secondary optics such as micro-lenses.

FIG. 13B illustrates an example of another LED array that may be formedaccording to certain embodiments of the hybrid bonding method describedherein, and that may include secondary optics such as AR coatings andgratings.

FIG. 14 shows a plot of the thermal expansion coefficient as a functionof the thermal conductivity for various materials.

FIG. 15 illustrates an example of an LED array in which run-out may becompensated by forming trenches between adjacent LEDs according tocertain embodiments.

FIG. 16 illustrates an example of another LED array in which run-out maybe compensated by forming trenches between adjacent LEDs and by formingcorresponding trenches through the substrate according to certainembodiments.

FIG. 17 illustrates an example of another LED array in which run-out maybe compensated by forming trenches between adjacent LEDs and by formingcorresponding full through the substrate according to certainembodiments.

FIG. 18 illustrates an example of another LED array in which run-out maybe compensated by changing the shape of components within an LED arrayaccording to certain embodiments.

FIGS. 19A and 19B show simulated plots of performance parameters for redmicro-LEDs having a vertical mesa shape and a maximum lateral dimensionof 10 μm.

FIGS. 20A and 20B show simulated plots of additional performanceparameters for red micro-LEDs having a vertical mesa shape and a maximumlateral dimension of 10 μm.

FIGS. 21A and 21B show simulated plots of performance parameters for redmicro-LEDs having a vertical mesa shape and a maximum lateral dimensionof 10 μm, along with red micro-LEDs having a parabolic mesa shape and amaximum lateral dimension of 3 μm.

FIGS. 22A and 22B show simulated plots of additional performanceparameters for red micro-LEDs having a vertical mesa shape and a maximumlateral dimension of 10 μm, along with red micro-LEDs having a parabolicmesa shape and a maximum lateral dimension of 3 μm.

FIG. 23 shows a simulated plot of brightness for red micro-LEDs having aparabolic mesa shape, an additional lens, an AR coating, and a maximumlateral dimension between 1 μm and 3 μm.

FIGS. 24A and 24B show simulated plots of performance parameters forgreen micro-LEDs having a vertical mesa shape and five quantum wells.

FIG. 25 shows a simulated plot of the total EQE for green micro-LEDs asa function of the current.

FIG. 26 shows a simulated plot of the total WPE for green micro-LEDs asa function of the current.

FIG. 27 shows a simulated plot of the brightness for green micro-LEDs asa function of the current.

FIGS. 28A and 28B show simulated plots of performance parameters forblue micro-LEDs having a vertical mesa shape.

FIGS. 29A and 29B show simulated plots of additional performanceparameters for blue micro-LEDs having a vertical mesa shape.

FIG. 30 shows a simulated plot of the brightness for blue micro-LEDs asa function of the current.

FIGS. 31A-31C illustrate an example of the use of alloy and strainfluctuations to confine lateral carriers according to certainembodiments.

FIG. 32 illustrates an example of ion implantation that may be performedaccording to certain embodiments.

FIGS. 33A, 33B, and 34 show various ion implantation depths formicro-LEDs according to certain embodiments.

FIGS. 35A and 35B show measurements of characteristics of micro-LEDs forwhich ion implantation has been performed according to certainembodiments.

FIGS. 36A-36C illustrate an example of quantum well intermixing that maybe performed according to certain embodiments.

FIG. 37 is a simplified block diagram of an electronic system of anexample of a near-eye display according to certain embodiments.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated may be employed without departing from theprinciples, or benefits touted, of this disclosure.

In the appended figures, similar components and/or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If only the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

DETAILED DESCRIPTION

The LEDs described herein may be used in conjunction with varioustechnologies, such as an artificial reality system. An artificialreality system, such as a head-mounted display (HMD) or heads-up display(HUD) system, generally includes a display configured to presentartificial images that depict objects in a virtual environment. Thedisplay may present virtual objects or combine images of real objectswith virtual objects, as in virtual reality (VR), augmented reality(AR), or mixed reality (MR) applications. For example, in an AR system,a user may view both displayed images of virtual objects (e.g.,computer-generated images (CGIs)) and the surrounding environment by,for example, seeing through transparent display glasses or lenses (oftenreferred to as optical see-through) or viewing displayed images of thesurrounding environment captured by a camera (often referred to as videosee-through). In some AR systems, the artificial images may be presentedto users using an LED-based display subsystem.

As used herein, the term “light emitting diode (LED)” refers to a lightsource that includes at least an n-type semiconductor layer, a p-typesemiconductor layer, and a light emitting region (i.e., active region)between the n-type semiconductor layer and the p-type semiconductorlayer. The light emitting region may include one or more semiconductorlayers that form one or more heterostructures, such as quantum wells. Insome embodiments, the light emitting region may include multiplesemiconductor layers that form one or more multiple-quantum-wells(MQWs), each including multiple (e.g., about 2 to 6) quantum wells.

As used herein, the term “micro-LED” or “μLED” refers to an LED that hasa chip where a linear dimension of the chip is less than about 200 μm,such as less than 100 μm, less than 50 μm, less than 20 μm, less than 10μm, or smaller. For example, the linear dimension of a micro-LED may beas small as 6 μm, 5 μm, 4 μm, 2 μm, or smaller. Some micro-LEDs may havea linear dimension (e.g., length or diameter) comparable to the minoritycarrier diffusion length. However, the disclosure herein is not limitedto micro-LEDs, and may also be applied to mini-LEDs and large LEDs.

As used herein, the term “bonding” may refer to various methods forphysically and/or electrically connecting two or more devices and/orwafers, such as adhesive bonding, metal-to-metal bonding, metal oxidebonding, wafer-to-wafer bonding, die-to-wafer bonding, hybrid bonding,soldering, under-bump metallization, and the like. For example, adhesivebonding may use a curable adhesive (e.g., an epoxy) to physically bondtwo or more devices and/or wafers through adhesion. Metal-to-metalbonding may include, for example, wire bonding or flip chip bondingusing soldering interfaces (e.g., pads or balls), conductive adhesive,or welded joints between metals. Metal oxide bonding may form a metaland oxide pattern on each surface, bond the oxide sections together, andthen bond the metal sections together to create a conductive path.Wafer-to-wafer bonding may bond two wafers (e.g., silicon wafers orother semiconductor wafers) without any intermediate layers and is basedon chemical bonds between the surfaces of the two wafers. Wafer-to-waferbonding may include wafer cleaning and other preprocessing, aligning andpre-bonding at room temperature, and annealing at elevated temperatures,such as about 250° C. or higher. Die-to-wafer bonding may use bumps onone wafer to align features of a pre-formed chip with drivers of awafer. Hybrid bonding may include, for example, wafer cleaning,high-precision alignment of contacts of one wafer with contacts ofanother wafer, dielectric bonding of dielectric materials within thewafers at room temperature, and metal bonding of the contacts byannealing at, for example, 250-300° C. or higher. As used herein, theterm “bump” may refer generically to a metal interconnect used or formedduring bonding.

In the following description, for the purposes of explanation, specificdetails are set forth in order to provide a thorough understanding ofexamples of the disclosure. However, it will be apparent that variousexamples may be practiced without these specific details. For example,devices, systems, structures, assemblies, methods, and other componentsmay be shown as components in block diagram form in order not to obscurethe examples in unnecessary detail. In other instances, well-knowndevices, processes, systems, structures, and techniques may be shownwithout necessary detail in order to avoid obscuring the examples. Thefigures and description are not intended to be restrictive. The termsand expressions that have been employed in this disclosure are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof. The word “example”is used herein to mean “serving as an example, instance, orillustration.” Any embodiment or design described herein as “example” isnot necessarily to be construed as preferred or advantageous over otherembodiments or designs.

FIG. 1 is a simplified block diagram of an example of an artificialreality system environment 100 including a near-eye display 120 inaccordance with certain embodiments. Artificial reality systemenvironment 100 shown in FIG. 1 may include near-eye display 120, anoptional external imaging device 150, and an optional input/outputinterface 140, each of which may be coupled to an optional console 110.While FIG. 1 shows an example of artificial reality system environment100 including one near-eye display 120, one external imaging device 150,and one input/output interface 140, any number of these components maybe included in artificial reality system environment 100, or any of thecomponents may be omitted. For example, there may be multiple near-eyedisplays 120 monitored by one or more external imaging devices 150 incommunication with console 110. In some configurations, artificialreality system environment 100 may not include external imaging device150, optional input/output interface 140, and optional console 110. Inalternative configurations, different or additional components may beincluded in artificial reality system environment 100.

Near-eye display 120 may be a head-mounted display that presents contentto a user. Examples of content presented by near-eye display 120 includeone or more of images, videos, audio, or any combination thereof. Insome embodiments, audio may be presented via an external device (e.g.,speakers and/or headphones) that receives audio information fromnear-eye display 120, console 110, or both, and presents audio databased on the audio information. Near-eye display 120 may include one ormore rigid bodies, which may be rigidly or non-rigidly coupled to eachother. A rigid coupling between rigid bodies may cause the coupled rigidbodies to act as a single rigid entity. A non-rigid coupling betweenrigid bodies may allow the rigid bodies to move relative to each other.In various embodiments, near-eye display 120 may be implemented in anysuitable form-factor, including a pair of glasses. Some embodiments ofnear-eye display 120 are further described below with respect to FIGS. 2and 3 . Additionally, in various embodiments, the functionalitydescribed herein may be used in a headset that combines images of anenvironment external to near-eye display 120 and artificial realitycontent (e.g., computer-generated images). Therefore, near-eye display120 may augment images of a physical, real-world environment external tonear-eye display 120 with generated content (e.g., images, video, sound,etc.) to present an augmented reality to a user.

In various embodiments, near-eye display 120 may include one or more ofdisplay electronics 122, display optics 124, and an eye-tracking unit130. In some embodiments, near-eye display 120 may also include one ormore locators 126, one or more position sensors 128, and an inertialmeasurement unit (IMU) 132. Near-eye display 120 may omit any ofeye-tracking unit 130, locators 126, position sensors 128, and IMU 132,or include additional elements in various embodiments. Additionally, insome embodiments, near-eye display 120 may include elements combiningthe function of various elements described in conjunction with FIG. 1 .

Display electronics 122 may display or facilitate the display of imagesto the user according to data received from, for example, console 110.In various embodiments, display electronics 122 may include one or moredisplay panels, such as a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, an inorganic light emitting diode (ILED)display, a micro light emitting diode (μLED) display, an active-matrixOLED display (AMOLED), a transparent OLED display (TOLED), or some otherdisplay. For example, in one implementation of near-eye display 120,display electronics 122 may include a front TOLED panel, a rear displaypanel, and an optical component (e.g., an attenuator, polarizer, ordiffractive or spectral film) between the front and rear display panels.Display electronics 122 may include pixels to emit light of apredominant color such as red, green, blue, white, or yellow. In someimplementations, display electronics 122 may display a three-dimensional(3D) image through stereoscopic effects produced by two-dimensionalpanels to create a subjective perception of image depth. For example,display electronics 122 may include a left display and a right displaypositioned in front of a user's left eye and right eye, respectively.The left and right displays may present copies of an image shiftedhorizontally relative to each other to create a stereoscopic effect(i.e., a perception of image depth by a user viewing the image).

In certain embodiments, display optics 124 may display image contentoptically (e.g., using optical waveguides and couplers) or magnify imagelight received from display electronics 122, correct optical errorsassociated with the image light, and present the corrected image lightto a user of near-eye display 120. In various embodiments, displayoptics 124 may include one or more optical elements, such as, forexample, a substrate, optical waveguides, an aperture, a Fresnel lens, aconvex lens, a concave lens, a filter, input/output couplers, or anyother suitable optical elements that may affect image light emitted fromdisplay electronics 122. Display optics 124 may include a combination ofdifferent optical elements as well as mechanical couplings to maintainrelative spacing and orientation of the optical elements in thecombination. One or more optical elements in display optics 124 may havean optical coating, such as an anti-reflective coating, a reflectivecoating, a filtering coating, or a combination of different opticalcoatings.

Magnification of the image light by display optics 124 may allow displayelectronics 122 to be physically smaller, weigh less, and consume lesspower than larger displays. Additionally, magnification may increase afield of view of the displayed content. The amount of magnification ofimage light by display optics 124 may be changed by adjusting, adding,or removing optical elements from display optics 124. In someembodiments, display optics 124 may project displayed images to one ormore image planes that may be further away from the user's eyes thannear-eye display 120.

Display optics 124 may also be designed to correct one or more types ofoptical errors, such as two-dimensional optical errors,three-dimensional optical errors, or any combination thereof.Two-dimensional errors may include optical aberrations that occur in twodimensions. Example types of two-dimensional errors may include barreldistortion, pincushion distortion, longitudinal chromatic aberration,and transverse chromatic aberration. Three-dimensional errors mayinclude optical errors that occur in three dimensions. Example types ofthree-dimensional errors may include spherical aberration, comaticaberration, field curvature, and astigmatism.

Locators 126 may be objects located in specific positions on near-eyedisplay 120 relative to one another and relative to a reference point onnear-eye display 120. In some implementations, console 110 may identifylocators 126 in images captured by external imaging device 150 todetermine the artificial reality headset's position, orientation, orboth. A locator 126 may be an LED, a corner cube reflector, a reflectivemarker, a type of light source that contrasts with an environment inwhich near-eye display 120 operates, or any combination thereof. Inembodiments where locators 126 are active components (e.g., LEDs orother types of light emitting devices), locators 126 may emit light inthe visible band (e.g., about 380 nm to 750 nm), in the infrared (IR)band (e.g., about 750 nm to 1 mm), in the ultraviolet band (e.g., about10 nm to about 380 μm), in another portion of the electromagneticspectrum, or in any combination of portions of the electromagneticspectrum.

External imaging device 150 may include one or more cameras, one or morevideo cameras, any other device capable of capturing images includingone or more of locators 126, or any combination thereof. Additionally,external imaging device 150 may include one or more filters (e.g., toincrease signal to noise ratio). External imaging device 150 may beconfigured to detect light emitted or reflected from locators 126 in afield of view of external imaging device 150. In embodiments wherelocators 126 include passive elements (e.g., retroreflectors), externalimaging device 150 may include a light source that illuminates some orall of locators 126, which may retro-reflect the light to the lightsource in external imaging device 150. Slow calibration data may becommunicated from external imaging device 150 to console 110, andexternal imaging device 150 may receive one or more calibrationparameters from console 110 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, sensor temperature, shutterspeed, aperture, etc.).

Position sensors 128 may generate one or more measurement signals inresponse to motion of near-eye display 120. Examples of position sensors128 may include accelerometers, gyroscopes, magnetometers, othermotion-detecting or error-correcting sensors, or any combinationthereof. For example, in some embodiments, position sensors 128 mayinclude multiple accelerometers to measure translational motion (e.g.,forward/back, up/down, or left/right) and multiple gyroscopes to measurerotational motion (e.g., pitch, yaw, or roll). In some embodiments,various position sensors may be oriented orthogonally to each other.

IMU 132 may be an electronic device that generates fast calibration databased on measurement signals received from one or more of positionsensors 128. Position sensors 128 may be located external to IMU 132,internal to IMU 132, or any combination thereof. Based on the one ormore measurement signals from one or more position sensors 128, IMU 132may generate fast calibration data indicating an estimated position ofnear-eye display 120 relative to an initial position of near-eye display120. For example, IMU 132 may integrate measurement signals receivedfrom accelerometers over time to estimate a velocity vector andintegrate the velocity vector over time to determine an estimatedposition of a reference point on near-eye display 120. Alternatively,IMU 132 may provide the sampled measurement signals to console 110,which may determine the fast calibration data. While the reference pointmay generally be defined as a point in space, in various embodiments,the reference point may also be defined as a point within near-eyedisplay 120 (e.g., a center of IMU 132).

Eye-tracking unit 130 may include one or more eye-tracking systems. Eyetracking may refer to determining an eye's position, includingorientation and location of the eye, relative to near-eye display 120.An eye-tracking system may include an imaging system to image one ormore eyes and may optionally include a light emitter, which may generatelight that is directed to an eye such that light reflected by the eyemay be captured by the imaging system. For example, eye-tracking unit130 may include a non-coherent or coherent light source (e.g., a laserdiode) emitting light in the visible spectrum or infrared spectrum, anda camera capturing the light reflected by the user's eye. As anotherexample, eye-tracking unit 130 may capture reflected radio waves emittedby a miniature radar unit. Eye-tracking unit 130 may use low-power lightemitters that emit light at frequencies and intensities that would notinjure the eye or cause physical discomfort. Eye-tracking unit 130 maybe arranged to increase contrast in images of an eye captured byeye-tracking unit 130 while reducing the overall power consumed byeye-tracking unit 130 (e.g., reducing power consumed by a light emitterand an imaging system included in eye-tracking unit 130). For example,in some implementations, eye-tracking unit 130 may consume less than 100milliwatts of power.

Near-eye display 120 may use the orientation of the eye to, e.g.,determine an inter-pupillary distance (IPD) of the user, determine gazedirection, introduce depth cues (e.g., blur image outside of the user'smain line of sight), collect heuristics on the user interaction in theVR media (e.g., time spent on any particular subject, object, or frameas a function of exposed stimuli), some other functions that are basedin part on the orientation of at least one of the user's eyes, or anycombination thereof. Because the orientation may be determined for botheyes of the user, eye-tracking unit 130 may be able to determine wherethe user is looking. For example, determining a direction of a user'sgaze may include determining a point of convergence based on thedetermined orientations of the user's left and right eyes. A point ofconvergence may be the point where the two foveal axes of the user'seyes intersect. The direction of the user's gaze may be the direction ofa line passing through the point of convergence and the mid-pointbetween the pupils of the user's eyes.

Input/output interface 140 may be a device that allows a user to sendaction requests to console 110. An action request may be a request toperform a particular action. For example, an action request may be tostart or to end an application or to perform a particular action withinthe application. Input/output interface 140 may include one or moreinput devices. Example input devices may include a keyboard, a mouse, agame controller, a glove, a button, a touch screen, or any othersuitable device for receiving action requests and communicating thereceived action requests to console 110. An action request received bythe input/output interface 140 may be communicated to console 110, whichmay perform an action corresponding to the requested action. In someembodiments, input/output interface 140 may provide haptic feedback tothe user in accordance with instructions received from console 110. Forexample, input/output interface 140 may provide haptic feedback when anaction request is received, or when console 110 has performed arequested action and communicates instructions to input/output interface140. In some embodiments, external imaging device 150 may be used totrack input/output interface 140, such as tracking the location orposition of a controller (which may include, for example, an IR lightsource) or a hand of the user to determine the motion of the user. Insome embodiments, near-eye display 120 may include one or more imagingdevices to track input/output interface 140, such as tracking thelocation or position of a controller or a hand of the user to determinethe motion of the user.

Console 110 may provide content to near-eye display 120 for presentationto the user in accordance with information received from one or more ofexternal imaging device 150, near-eye display 120, and input/outputinterface 140. In the example shown in FIG. 1 , console 110 may includean application store 112, a headset tracking module 114, an artificialreality engine 116, and an eye-tracking module 118. Some embodiments ofconsole 110 may include different or additional modules than thosedescribed in conjunction with FIG. 1 . Functions further described belowmay be distributed among components of console 110 in a different mannerthan is described here.

In some embodiments, console 110 may include a processor and anon-transitory computer-readable storage medium storing instructionsexecutable by the processor. The processor may include multipleprocessing units executing instructions in parallel. The non-transitorycomputer-readable storage medium may be any memory, such as a hard diskdrive, a removable memory, or a solid-state drive (e.g., flash memory ordynamic random access memory (DRAM)). In various embodiments, themodules of console 110 described in conjunction with FIG. 1 may beencoded as instructions in the non-transitory computer-readable storagemedium that, when executed by the processor, cause the processor toperform the functions further described below.

Application store 112 may store one or more applications for executionby console 110. An application may include a group of instructions that,when executed by a processor, generates content for presentation to theuser. Content generated by an application may be in response to inputsreceived from the user via movement of the user's eyes or inputsreceived from the input/output interface 140. Examples of theapplications may include gaming applications, conferencing applications,video playback application, or other suitable applications.

Headset tracking module 114 may track movements of near-eye display 120using slow calibration information from external imaging device 150. Forexample, headset tracking module 114 may determine positions of areference point of near-eye display 120 using observed locators from theslow calibration information and a model of near-eye display 120.Headset tracking module 114 may also determine positions of a referencepoint of near-eye display 120 using position information from the fastcalibration information. Additionally, in some embodiments, headsettracking module 114 may use portions of the fast calibrationinformation, the slow calibration information, or any combinationthereof, to predict a future location of near-eye display 120. Headsettracking module 114 may provide the estimated or predicted futureposition of near-eye display 120 to artificial reality engine 116.

Artificial reality engine 116 may execute applications within artificialreality system environment 100 and receive position information ofnear-eye display 120, acceleration information of near-eye display 120,velocity information of near-eye display 120, predicted future positionsof near-eye display 120, or any combination thereof from headsettracking module 114. Artificial reality engine 116 may also receiveestimated eye position and orientation information from eye-trackingmodule 118. Based on the received information, artificial reality engine116 may determine content to provide to near-eye display 120 forpresentation to the user. For example, if the received informationindicates that the user has looked to the left, artificial realityengine 116 may generate content for near-eye display 120 that mirrorsthe user's eye movement in a virtual environment. Additionally,artificial reality engine 116 may perform an action within anapplication executing on console 110 in response to an action requestreceived from input/output interface 140, and provide feedback to theuser indicating that the action has been performed. The feedback may bevisual or audible feedback via near-eye display 120 or haptic feedbackvia input/output interface 140.

Eye-tracking module 118 may receive eye-tracking data from eye-trackingunit 130 and determine the position of the user's eye based on the eyetracking data. The position of the eye may include an eye's orientation,location, or both relative to near-eye display 120 or any elementthereof. Because the eye's axes of rotation change as a function of theeye's location in its socket, determining the eye's location in itssocket may allow eye-tracking module 118 to more accurately determinethe eye's orientation.

FIG. 2 is a perspective view of an example of a near-eye display in theform of an HMD device 200 for implementing some of the examplesdisclosed herein. HMD device 200 may be a part of, e.g., a VR system, anAR system, an MR system, or any combination thereof. HMD device 200 mayinclude a body 220 and a head strap 230. FIG. 2 shows a bottom side 223,a front side 225, and a left side 227 of body 220 in the perspectiveview. Head strap 230 may have an adjustable or extendible length. Theremay be a sufficient space between body 220 and head strap 230 of HMDdevice 200 for allowing a user to mount HMD device 200 onto the user'shead. In various embodiments, HMD device 200 may include additional,fewer, or different components. For example, in some embodiments, HMDdevice 200 may include eyeglass temples and temple tips as shown in, forexample, FIG. 3 below, rather than head strap 230.

HMD device 200 may present to a user media including virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements. Examples of the media presented by HMDdevice 200 may include images (e.g., two-dimensional (2D) orthree-dimensional (3D) images), videos (e.g., 2D or 3D videos), audio,or any combination thereof. The images and videos may be presented toeach eye of the user by one or more display assemblies (not shown inFIG. 2 ) enclosed in body 220 of HMD device 200. In various embodiments,the one or more display assemblies may include a single electronicdisplay panel or multiple electronic display panels (e.g., one displaypanel for each eye of the user). Examples of the electronic displaypanel(s) may include, for example, an LCD, an OLED display, an ILEDdisplay, a μLED display, an AMOLED, a TOLED, some other display, or anycombination thereof. HMD device 200 may include two eye box regions.

In some implementations, HMD device 200 may include various sensors (notshown), such as depth sensors, motion sensors, position sensors, and eyetracking sensors. Some of these sensors may use a structured lightpattern for sensing. In some implementations, HMD device 200 may includean input/output interface for communicating with a console. In someimplementations, HMD device 200 may include a virtual reality engine(not shown) that can execute applications within HMD device 200 andreceive depth information, position information, accelerationinformation, velocity information, predicted future positions, or anycombination thereof of HMD device 200 from the various sensors. In someimplementations, the information received by the virtual reality enginemay be used for producing a signal (e.g., display instructions) to theone or more display assemblies. In some implementations, HMD device 200may include locators (not shown, such as locators 126) located in fixedpositions on body 220 relative to one another and relative to areference point. Each of the locators may emit light that is detectableby an external imaging device.

FIG. 3 is a perspective view of an example of a near-eye display 300 inthe form of a pair of glasses for implementing some of the examplesdisclosed herein. Near-eye display 300 may be a specific implementationof near-eye display 120 of FIG. 1 , and may be configured to operate asa virtual reality display, an augmented reality display, and/or a mixedreality display.

Near-eye display 300 may include a frame 305 and a display 310. Display310 may be configured to present content to a user. In some embodiments,display 310 may include display electronics and/or display optics. Forexample, as described above with respect to near-eye display 120 of FIG.1 , display 310 may include an LCD display panel, an LED display panel,or an optical display panel (e.g., a waveguide display assembly).

Near-eye display 300 may further include various sensors 350 a, 350 b,350 c, 350 d, and 350 e on or within frame 305. In some embodiments,sensors 350 a-350 e may include one or more depth sensors, motionsensors, position sensors, inertial sensors, or ambient light sensors.In some embodiments, sensors 350 a-350 e may include one or more imagesensors configured to generate image data representing different fieldsof views in different directions. In some embodiments, sensors 350 a-350e may be used as input devices to control or influence the displayedcontent of near-eye display 300, and/or to provide an interactiveVR/AR/MR experience to a user of near-eye display 300. In someembodiments, sensors 350 a-350 e may also be used for stereoscopicimaging.

In some embodiments, near-eye display 300 may further include one ormore illuminators 330 to project light into the physical environment.The projected light may be associated with different frequency bands(e.g., visible light, infra-red light, ultra-violet light, etc.), andmay serve various purposes. For example, illuminator(s) 330 may projectlight in a dark environment (or in an environment with low intensity ofinfra-red light, ultra-violet light, etc.) to assist sensors 350 a-350 ein capturing images of different objects within the dark environment. Insome embodiments, illuminator(s) 330 may be used to project certainlight patterns onto the objects within the environment. In someembodiments, illuminator(s) 330 may be used as locators, such aslocators 126 described above with respect to FIG. 1 .

In some embodiments, near-eye display 300 may also include ahigh-resolution camera 340. Camera 340 may capture images of thephysical environment in the field of view. The captured images may beprocessed, for example, by a virtual reality engine (e.g., artificialreality engine 116 of FIG. 1 ) to add virtual objects to the capturedimages or modify physical objects in the captured images, and theprocessed images may be displayed to the user by display 310 for AR orMR applications.

FIG. 4 illustrates an example of an optical see-through augmentedreality system 400 including a waveguide display according to certainembodiments. Augmented reality system 400 may include a projector 410and a combiner 415. Projector 410 may include a light source or imagesource 412 and projector optics 414. In some embodiments, light sourceor image source 412 may include one or more micro-LED devices describedabove. In some embodiments, image source 412 may include a plurality ofpixels that displays virtual objects, such as an LCD display panel or anLED display panel. In some embodiments, image source 412 may include alight source that generates coherent or partially coherent light. Forexample, image source 412 may include a laser diode, a vertical cavitysurface emitting laser, an LED, and/or a micro-LED described above. Insome embodiments, image source 412 may include a plurality of lightsources (e.g., an array of micro-LEDs described above), each emitting amonochromatic image light corresponding to a primary color (e.g., red,green, or blue). In some embodiments, image source 412 may include threetwo-dimensional arrays of micro-LEDs, where each two-dimensional arrayof micro-LEDs may include micro-LEDs configured to emit light of aprimary color (e.g., red, green, or blue). In some embodiments, imagesource 412 may include an optical pattern generator, such as a spatiallight modulator. Projector optics 414 may include one or more opticalcomponents that can condition the light from image source 412, such asexpanding, collimating, scanning, or projecting light from image source412 to combiner 415. The one or more optical components may include, forexample, one or more lenses, liquid lenses, mirrors, apertures, and/orgratings. For example, in some embodiments, image source 412 may includeone or more one-dimensional arrays or elongated two-dimensional arraysof micro-LEDs, and projector optics 414 may include one or moreone-dimensional scanners (e.g., micro-mirrors or prisms) configured toscan the one-dimensional arrays or elongated two-dimensional arrays ofmicro-LEDs to generate image frames. In some embodiments, projectoroptics 414 may include a liquid lens (e.g., a liquid crystal lens) witha plurality of electrodes that allows scanning of the light from imagesource 412.

Combiner 415 may include an input coupler 430 for coupling light fromprojector 410 into a substrate 420 of combiner 415. Combiner 415 maytransmit at least 50% of light in a first wavelength range and reflectat least 25% of light in a second wavelength range. For example, thefirst wavelength range may be visible light from about 400 nm to about650 nm, and the second wavelength range may be in the infrared band, forexample, from about 800 nm to about 1000 nm. Input coupler 430 mayinclude a volume holographic grating, a diffractive optical element(DOE) (e.g., a surface-relief grating), a slanted surface of substrate420, or a refractive coupler (e.g., a wedge or a prism). For example,input coupler 430 may include a reflective volume Bragg grating or atransmissive volume Bragg grating. Input coupler 430 may have a couplingefficiency of greater than 30%, 50%, 75%, 90%, or higher for visiblelight. Light coupled into substrate 420 may propagate within substrate420 through, for example, total internal reflection (TIR). Substrate 420may be in the form of a lens of a pair of eyeglasses. Substrate 420 mayhave a flat or a curved surface, and may include one or more types ofdielectric materials, such as glass, quartz, plastic, polymer,poly(methyl methacrylate) (PMMA), crystal, or ceramic. A thickness ofthe substrate may range from, for example, less than about 1 mm to about10 mm or more. Substrate 420 may be transparent to visible light.

Substrate 420 may include or may be coupled to a plurality of outputcouplers 440, each configured to extract at least a portion of the lightguided by and propagating within substrate 420 from substrate 420, anddirect extracted light 460 to an eyebox 495 where an eye 490 of the userof augmented reality system 400 may be located when augmented realitysystem 400 is in use. The plurality of output couplers 440 may replicatethe exit pupil to increase the size of eyebox 495 such that thedisplayed image is visible in a larger area. As input coupler 430,output couplers 440 may include grating couplers (e.g., volumeholographic gratings or surface-relief gratings), other diffractionoptical elements (DOEs), prisms, etc. For example, output couplers 440may include reflective volume Bragg gratings or transmissive volumeBragg gratings. Output couplers 440 may have different coupling (e.g.,diffraction) efficiencies at different locations. Substrate 420 may alsoallow light 450 from the environment in front of combiner 415 to passthrough with little or no loss. Output couplers 440 may also allow light450 to pass through with little loss. For example, in someimplementations, output couplers 440 may have a very low diffractionefficiency for light 450 such that light 450 may be refracted orotherwise pass through output couplers 440 with little loss, and thusmay have a higher intensity than extracted light 460. In someimplementations, output couplers 440 may have a high diffractionefficiency for light 450 and may diffract light 450 in certain desireddirections (i.e., diffraction angles) with little loss. As a result, theuser may be able to view combined images of the environment in front ofcombiner 415 and images of virtual objects projected by projector 410.

FIG. 5A illustrates an example of a near-eye display (NED) device 500including a waveguide display 530 according to certain embodiments. NEDdevice 500 may be an example of near-eye display 120, augmented realitysystem 400, or another type of display device. NED device 500 mayinclude a light source 510, projection optics 520, and waveguide display530. Light source 510 may include multiple panels of light emitters fordifferent colors, such as a panel of red light emitters 512, a panel ofgreen light emitters 514, and a panel of blue light emitters 516. Thered light emitters 512 are organized into an array; the green lightemitters 514 are organized into an array; and the blue light emitters516 are organized into an array. The dimensions and pitches of lightemitters in light source 510 may be small. For example, each lightemitter may have a diameter less than 2 μm (e.g., about 1.2 μm) and thepitch may be less than 2 μm (e.g., about 1.5 μm). As such, the number oflight emitters in each red light emitters 512, green light emitters 514,and blue light emitters 516 can be equal to or greater than the numberof pixels in a display image, such as 960×720, 1280×720, 1440×1080,1920×1080, 2160×1080, or 2560×1080 pixels. Thus, a display image may begenerated simultaneously by light source 510. A scanning element may notbe used in NED device 500.

Before reaching waveguide display 530, the light emitted by light source510 may be conditioned by projection optics 520, which may include alens array. Projection optics 520 may collimate or focus the lightemitted by light source 510 to waveguide display 530, which may includea coupler 532 for coupling the light emitted by light source 510 intowaveguide display 530. The light coupled into waveguide display 530 maypropagate within waveguide display 530 through, for example, totalinternal reflection as described above with respect to FIG. 4 . Coupler532 may also couple portions of the light propagating within waveguidedisplay 530 out of waveguide display 530 and towards user's eye 590.

FIG. 5B illustrates an example of a near-eye display (NED) device 550including a waveguide display 580 according to certain embodiments. Insome embodiments, NED device 550 may use a scanning mirror 570 toproject light from a light source 540 to an image field where a user'seye 590 may be located. NED device 550 may be an example of near-eyedisplay 120, augmented reality system 400, or another type of displaydevice. Light source 540 may include one or more rows or one or morecolumns of light emitters of different colors, such as multiple rows ofred light emitters 542, multiple rows of green light emitters 544, andmultiple rows of blue light emitters 546. For example, red lightemitters 542, green light emitters 544, and blue light emitters 546 mayeach include N rows, each row including, for example, 2560 lightemitters (pixels). The red light emitters 542 are organized into anarray; the green light emitters 544 are organized into an array; and theblue light emitters 546 are organized into an array. In someembodiments, light source 540 may include a single line of lightemitters for each color. In some embodiments, light source 540 mayinclude multiple columns of light emitters for each of red, green, andblue colors, where each column may include, for example, 1080 lightemitters. In some embodiments, the dimensions and/or pitches of thelight emitters in light source 540 may be relatively large (e.g., about3-5 μm) and thus light source 540 may not include sufficient lightemitters for simultaneously generating a full display image. Forexample, the number of light emitters for a single color may be fewerthan the number of pixels (e.g., 2560×1080 pixels) in a display image.The light emitted by light source 540 may be a set of collimated ordiverging beams of light.

Before reaching scanning mirror 570, the light emitted by light source540 may be conditioned by various optical devices, such as collimatinglenses or a freeform optical element 560. Freeform optical element 560may include, for example, a multi-facet prism or another light foldingelement that may direct the light emitted by light source 540 towardsscanning mirror 570, such as changing the propagation direction of thelight emitted by light source 540 by, for example, about 90° or larger.In some embodiments, freeform optical element 560 may be rotatable toscan the light. Scanning mirror 570 and/or freeform optical element 560may reflect and project the light emitted by light source 540 towaveguide display 580, which may include a coupler 582 for coupling thelight emitted by light source 540 into waveguide display 580. The lightcoupled into waveguide display 580 may propagate within waveguidedisplay 580 through, for example, total internal reflection as describedabove with respect to FIG. 4 . Coupler 582 may also couple portions ofthe light propagating within waveguide display 580 out of waveguidedisplay 580 and towards user's eye 590.

Scanning mirror 570 may include a microelectromechanical system (MEMS)mirror or any other suitable mirrors. Scanning mirror 570 may rotate toscan in one or two dimensions. As scanning mirror 570 rotates, the lightemitted by light source 540 may be directed to a different area ofwaveguide display 580 such that a full display image may be projectedonto waveguide display 580 and directed to user's eye 590 by waveguidedisplay 580 in each scanning cycle. For example, in embodiments wherelight source 540 includes light emitters for all pixels in one or morerows or columns, scanning mirror 570 may be rotated in the column or rowdirection (e.g., x or y direction) to scan an image. In embodimentswhere light source 540 includes light emitters for some but not allpixels in one or more rows or columns, scanning mirror 570 may berotated in both the row and column directions (e.g., both x and ydirections) to project a display image (e.g., using a raster-typescanning pattern).

NED device 550 may operate in predefined display periods. A displayperiod (e.g., display cycle) may refer to a duration of time in which afull image is scanned or projected. For example, a display period may bea reciprocal of the desired frame rate. In NED device 550 that includesscanning mirror 570, the display period may also be referred to as ascanning period or scanning cycle. The light generation by light source540 may be synchronized with the rotation of scanning mirror 570. Forexample, each scanning cycle may include multiple scanning steps, wherelight source 540 may generate a different light pattern in eachrespective scanning step.

In each scanning cycle, as scanning mirror 570 rotates, a display imagemay be projected onto waveguide display 580 and user's eye 590. Theactual color value and light intensity (e.g., brightness) of a givenpixel location of the display image may be an average of the light beamsof the three colors (e.g., red, green, and blue) illuminating the pixellocation during the scanning period. After completing a scanning period,scanning mirror 570 may revert back to the initial position to projectlight for the first few rows of the next display image or may rotate ina reverse direction or scan pattern to project light for the nextdisplay image, where a new set of driving signals may be fed to lightsource 540. The same process may be repeated as scanning mirror 570rotates in each scanning cycle. As such, different images may beprojected to user's eye 590 in different scanning cycles.

FIG. 6 illustrates an example of an image source assembly 610 in anear-eye display system 600 according to certain embodiments. Imagesource assembly 610 may include, for example, a display panel 640 thatmay generate display images to be projected to the user's eyes, and aprojector 650 that may project the display images generated by displaypanel 640 to a waveguide display as described above with respect toFIGS. 4-5B. Display panel 640 may include a light source 642 and adriver circuit 644 for light source 642. Light source 642 may include,for example, light source 510 or 540. Projector 650 may include, forexample, freeform optical element 560, scanning mirror 570, and/orprojection optics 520 described above. Near-eye display system 600 mayalso include a controller 620 that synchronously controls light source642 and projector 650 (e.g., scanning mirror 570). Image source assembly610 may generate and output an image light to a waveguide display (notshown in FIG. 6 ), such as waveguide display 530 or 580. As describedabove, the waveguide display may receive the image light at one or moreinput-coupling elements, and guide the received image light to one ormore output-coupling elements. The input and output coupling elementsmay include, for example, a diffraction grating, a holographic grating,a prism, or any combination thereof. The input-coupling element may bechosen such that total internal reflection occurs with the waveguidedisplay. The output-coupling element may couple portions of the totalinternally reflected image light out of the waveguide display.

As described above, light source 642 may include a plurality of lightemitters arranged in an array or a matrix. Each light emitter may emitmonochromatic light, such as red light, blue light, green light,infra-red light, and the like. While RGB colors are often discussed inthis disclosure, embodiments described herein are not limited to usingred, green, and blue as primary colors. Other colors can also be used asthe primary colors of near-eye display system 600. In some embodiments,a display panel in accordance with an embodiment may use more than threeprimary colors. Each pixel in light source 642 may include threesubpixels that include a red micro-LED, a green micro-LED, and a bluemicro-LED. A semiconductor LED generally includes an active lightemitting layer within multiple layers of semiconductor materials. Themultiple layers of semiconductor materials may include differentcompound materials or a same base material with different dopants and/ordifferent doping densities. For example, the multiple layers ofsemiconductor materials may include an n-type material layer, an activeregion that may include hetero-structures (e.g., one or more quantumwells), and a p-type material layer. The multiple layers ofsemiconductor materials may be grown on a surface of a substrate havinga certain orientation. In some embodiments, to increase light extractionefficiency, a mesa that includes at least some of the layers ofsemiconductor materials may be formed.

Controller 620 may control the image rendering operations of imagesource assembly 610, such as the operations of light source 642 and/orprojector 650. For example, controller 620 may determine instructionsfor image source assembly 610 to render one or more display images. Theinstructions may include display instructions and scanning instructions.In some embodiments, the display instructions may include an image file(e.g., a bitmap file). The display instructions may be received from,for example, a console, such as console 110 described above with respectto FIG. 1 . The scanning instructions may be used by image sourceassembly 610 to generate image light. The scanning instructions mayspecify, for example, a type of a source of image light (e.g.,monochromatic or polychromatic), a scanning rate, an orientation of ascanning apparatus, one or more illumination parameters, or anycombination thereof. Controller 620 may include a combination ofhardware, software, and/or firmware not shown here so as not to obscureother aspects of the present disclosure.

In some embodiments, controller 620 may be a graphics processing unit(GPU) of a display device. In other embodiments, controller 620 may beother kinds of processors. The operations performed by controller 620may include taking content for display and dividing the content intodiscrete sections. Controller 620 may provide to light source 642scanning instructions that include an address corresponding to anindividual source element of light source 642 and/or an electrical biasapplied to the individual source element. Controller 620 may instructlight source 642 to sequentially present the discrete sections usinglight emitters corresponding to one or more rows of pixels in an imageultimately displayed to the user. Controller 620 may also instructprojector 650 to perform different adjustments of the light. Forexample, controller 620 may control projector 650 to scan the discretesections to different areas of a coupling element of the waveguidedisplay (e.g., waveguide display 580) as described above with respect toFIG. 5B. As such, at the exit pupil of the waveguide display, eachdiscrete portion is presented in a different respective location. Whileeach discrete section is presented at a different respective time, thepresentation and scanning of the discrete sections occur fast enoughsuch that a user's eye may integrate the different sections into asingle image or series of images.

Image processor 630 may be a general-purpose processor and/or one ormore application-specific circuits that are dedicated to performing thefeatures described herein. In one embodiment, a general-purposeprocessor may be coupled to a memory to execute software instructionsthat cause the processor to perform certain processes described herein.In another embodiment, image processor 630 may be one or more circuitsthat are dedicated to performing certain features. While image processor630 in FIG. 6 is shown as a stand-alone unit that is separate fromcontroller 620 and driver circuit 644, image processor 630 may be asub-unit of controller 620 or driver circuit 644 in other embodiments.In other words, in those embodiments, controller 620 or driver circuit644 may perform various image processing functions of image processor630. Image processor 630 may also be referred to as an image processingcircuit.

In the example shown in FIG. 6 , light source 642 may be driven bydriver circuit 644, based on data or instructions (e.g., display andscanning instructions) sent from controller 620 or image processor 630.In one embodiment, driver circuit 644 may include a circuit panel thatconnects to and mechanically holds various light emitters of lightsource 642. Light source 642 may emit light in accordance with one ormore illumination parameters that are set by the controller 620 andpotentially adjusted by image processor 630 and driver circuit 644. Anillumination parameter may be used by light source 642 to generatelight. An illumination parameter may include, for example, sourcewavelength, pulse rate, pulse amplitude, beam type (continuous orpulsed), other parameter(s) that may affect the emitted light, or anycombination thereof. In some embodiments, the source light generated bylight source 642 may include multiple beams of red light, green light,and blue light, or any combination thereof.

Projector 650 may perform a set of optical functions, such as focusing,combining, conditioning, or scanning the image light generated by lightsource 642. In some embodiments, projector 650 may include a combiningassembly, a light conditioning assembly, or a scanning mirror assembly.Projector 650 may include one or more optical components that opticallyadjust and potentially re-direct the light from light source 642. Oneexample of the adjustment of light may include conditioning the light,such as expanding, collimating, correcting for one or more opticalerrors (e.g., field curvature, chromatic aberration, etc.), some otheradjustments of the light, or any combination thereof. The opticalcomponents of projector 650 may include, for example, lenses, mirrors,apertures, gratings, or any combination thereof.

Projector 650 may redirect image light via its one or more reflectiveand/or refractive portions so that the image light is projected atcertain orientations toward the waveguide display. The location wherethe image light is redirected toward the waveguide display may depend onspecific orientations of the one or more reflective and/or refractiveportions. In some embodiments, projector 650 includes a single scanningmirror that scans in at least two dimensions. In other embodiments,projector 650 may include a plurality of scanning mirrors that each scanin directions orthogonal to each other. Projector 650 may perform araster scan (horizontally or vertically), a bi-resonant scan, or anycombination thereof. In some embodiments, projector 650 may perform acontrolled vibration along the horizontal and/or vertical directionswith a specific frequency of oscillation to scan along two dimensionsand generate a two-dimensional projected image of the media presented touser's eyes. In other embodiments, projector 650 may include a lens orprism that may serve similar or the same function as one or morescanning mirrors. In some embodiments, image source assembly 610 may notinclude a projector, where the light emitted by light source 642 may bedirectly incident on the waveguide display.

In semiconductor LEDs, photons are usually generated at a certaininternal quantum efficiency through the recombination of electrons andholes within an active region (e.g., one or more semiconductor layers),where the internal quantum efficiency is the proportion of the radiativeelectron-hole recombination in the active region that emits photons. Thegenerated light may then be extracted from the LEDs in a particulardirection or within a particular solid angle. The ratio between thenumber of emitted photons extracted from an LED and the number ofelectrons passing through the LED is referred to as the external quantumefficiency, which describes how efficiently the LED converts injectedelectrons to photons that are extracted from the device.

The external quantum efficiency may be proportional to the injectionefficiency, the internal quantum efficiency, and the extractionefficiency. The injection efficiency refers to the proportion ofelectrons passing through the device that are injected into the activeregion. The extraction efficiency is the proportion of photons generatedin the active region that escape from the device. For LEDs, and inparticular, micro-LEDs with reduced physical dimensions, improving theinternal and external quantum efficiency and/or controlling the emissionspectrum may be challenging. In some embodiments, to increase the lightextraction efficiency, a mesa that includes at least some of the layersof semiconductor materials may be formed.

FIG. 7A illustrates an example of an LED 700 having a vertical mesastructure. LED 700 may be a light emitter in light source 510, 540, or642. LED 700 may be a micro-LED made of inorganic materials, such asmultiple layers of semiconductor materials. The layered semiconductorlight emitting device may include multiple layers of III-V semiconductormaterials. A III-V semiconductor material may include one or more GroupIII elements, such as aluminum (Al), gallium (Ga), or indium (In), incombination with a Group V element, such as nitrogen (N), phosphorus(P), arsenic (As), or antimony (Sb). When the Group V element of theIII-V semiconductor material includes nitrogen, the III-V semiconductormaterial is referred to as a III-nitride material. The layeredsemiconductor light emitting device may be manufactured by growingmultiple epitaxial layers on a substrate using techniques such asvapor-phase epitaxy (VPE), liquid-phase epitaxy (LPE), molecular beamepitaxy (MBE), or metalorganic chemical vapor deposition (MOCVD). Forexample, the layers of the semiconductor materials may be grownlayer-by-layer on a substrate with a certain crystal lattice orientation(e.g., polar, nonpolar, or semi-polar orientation), such as a GaN, GaAs,or GaP substrate, or a substrate including, but not limited to,sapphire, silicon carbide, silicon, zinc oxide, boron nitride, lithiumaluminate, lithium niobate, germanium, aluminum nitride, lithiumgallate, partially substituted spinels, or quaternary tetragonal oxidessharing the beta-LiAlO₂ structure, where the substrate may be cut in aspecific direction to expose a specific plane as the growth surface.

In the example shown in FIG. 7A, LED 700 may include a substrate 710,which may include, for example, a sapphire substrate or a GaN substrate.A semiconductor layer 720 may be grown on substrate 710. Semiconductorlayer 720 may include a III-V material, such as GaN, and may be p-doped(e.g., with Mg, Ca, Zn, or Be) or n-doped (e.g., with Si or Ge). One ormore active layers 730 may be grown on semiconductor layer 720 to forman active region. Active layer 730 may include III-V materials, such asone or more InGaN layers, one or more AlInGaP layers, and/or one or moreGaN layers, which may form one or more heterostructures, such as one ormore quantum wells or MQWs. A semiconductor layer 740 may be grown onactive layer 730. Semiconductor layer 740 may include a III-V material,such as GaN, and may be p-doped (e.g., with Mg, Ca, Zn, or Be) orn-doped (e.g., with Si or Ge). One of semiconductor layer 720 andsemiconductor layer 740 may be a p-type layer and the other one may bean n-type layer. Semiconductor layer 720 and semiconductor layer 740sandwich active layer 730 to form the light emitting region. Forexample, LED 700 may include a layer of InGaN situated between a layerof p-type GaN doped with magnesium and a layer of n-type GaN doped withsilicon or oxygen. In some embodiments, LED 700 may include a layer ofAlInGaP situated between a layer of p-type AlInGaP doped with zinc ormagnesium and a layer of n-type AlInGaP doped with selenium, silicon, ortellurium.

In some embodiments, an electron-blocking layer (EBL) (not shown in FIG.7A) may be grown to form a layer between active layer 730 and at leastone of semiconductor layer 720 or semiconductor layer 740. The EBL mayreduce the electron leakage current and improve the efficiency of theLED. In some embodiments, a heavily-doped semiconductor layer 750, suchas a P⁺ or P⁺⁺ semiconductor layer, may be formed on semiconductor layer740 and act as a contact layer for forming an ohmic contact and reducingthe contact impedance of the device. In some embodiments, a conductivelayer 760 may be formed on heavily-doped semiconductor layer 750.Conductive layer 760 may include, for example, an indium tin oxide (ITO)or Al/Ni/Au film. In one example, conductive layer 760 may include atransparent ITO layer.

To make contact with semiconductor layer 720 (e.g., an n-GaN layer) andto more efficiently extract light emitted by active layer 730 from LED700, the semiconductor material layers (including heavily-dopedsemiconductor layer 750, semiconductor layer 740, active layer 730, andsemiconductor layer 720) may be etched to expose semiconductor layer 720and to form a mesa structure that includes layers 720-760. The mesastructure may confine the carriers within the device. Etching the mesastructure may lead to the formation of mesa sidewalls 732 that may beorthogonal to the growth planes. A passivation layer 770 may be formedon sidewalls 732 of the mesa structure. Passivation layer 770 mayinclude an oxide layer, such as a SiO₂ layer, and may act as a reflectorto reflect emitted light out of LED 700. A contact layer 780, which mayinclude a metal layer, such as Al, Au, Ni, Ti, or any combinationthereof, may be formed on semiconductor layer 720 and may act as anelectrode of LED 700. In addition, another contact layer 790, such as anAl/Ni/Au metal layer, may be formed on conductive layer 760 and may actas another electrode of LED 700.

When a voltage signal is applied to contact layers 780 and 790,electrons and holes may recombine in active layer 730, where therecombination of electrons and holes may cause photon emission. Thewavelength and energy of the emitted photons may depend on the energybandgap between the valence band and the conduction band in active layer730. For example, InGaN active layers may emit green or blue light,AlGaN active layers may emit blue to ultraviolet light, while AlInGaPactive layers may emit red, orange, yellow, or green light. The emittedphotons may be reflected by passivation layer 770 and may exit LED 700from the top (e.g., conductive layer 760 and contact layer 790) orbottom (e.g., substrate 710).

In some embodiments, LED 700 may include one or more other components,such as a lens, on the light emission surface, such as substrate 710, tofocus or collimate the emitted light or couple the emitted light into awaveguide. In some embodiments, an LED may include a mesa of anothershape, such as planar, conical, semi-parabolic, or parabolic, and a basearea of the mesa may be circular, rectangular, hexagonal, or triangular.For example, the LED may include a mesa of a curved shape (e.g.,paraboloid shape) and/or a non-curved shape (e.g., conic shape). Themesa may be truncated or non-truncated.

FIG. 7B is a cross-sectional view of an example of an LED 705 having aparabolic mesa structure. Similar to LED 700, LED 705 may includemultiple layers of semiconductor materials, such as multiple layers ofIII-V semiconductor materials. The semiconductor material layers may beepitaxially grown on a substrate 715, such as a GaN substrate or asapphire substrate. For example, a semiconductor layer 725 may be grownon substrate 715.

Semiconductor layer 725 may include a III-V material, such as GaN, andmay be p-doped (e.g., with Mg, Ca, Zn, or Be) or n-doped (e.g., with Sior Ge). One or more active layer 735 may be grown on semiconductor layer725. Active layer 735 may include III-V materials, such as one or moreInGaN layers, one or more AlInGaP layers, and/or one or more GaN layers,which may form one or more heterostructures, such as one or more quantumwells. A semiconductor layer 745 may be grown on active layer 735.Semiconductor layer 745 may include a III-V material, such as GaN, andmay be p-doped (e.g., with Mg, Ca, Zn, or Be) or n-doped (e.g., with Sior Ge). One of semiconductor layer 725 and semiconductor layer 745 maybe a p-type layer and the other one may be an n-type layer.

To make contact with semiconductor layer 725 (e.g., an n-type GaN layer)and to more efficiently extract light emitted by active layer 735 fromLED 705, the semiconductor layers may be etched to expose semiconductorlayer 725 and to form a mesa structure that includes layers 725-745. Themesa structure may confine carriers within the injection area of thedevice. Etching the mesa structure may lead to the formation of mesaside walls (also referred to herein as facets) that may be non-parallelwith, or in some cases, orthogonal, to the growth planes associated withcrystalline growth of layers 725-745.

As shown in FIG. 7B, LED 705 may have a mesa structure that includes aflat top. A dielectric layer 775 (e.g., SiO₂ or SiNx) may be formed onthe facets of the mesa structure. In some embodiments, dielectric layer775 may include multiple layers of dielectric materials. In someembodiments, a metal layer 795 may be formed on dielectric layer 775.Metal layer 795 may include one or more metal or metal alloy materials,such as aluminum (Al), silver (Ag), gold (Au), platinum (Pt), titanium(Ti), copper (Cu), or any combination thereof. Dielectric layer 775 andmetal layer 795 may form a mesa reflector that can reflect light emittedby active layer 735 toward substrate 715. In some embodiments, the mesareflector may be parabolic-shaped to act as a parabolic reflector thatmay at least partially collimate the emitted light.

Electrical contact 765 and electrical contact 785 may be formed onsemiconductor layer 745 and semiconductor layer 725, respectively, toact as electrodes. Electrical contact 765 and electrical contact 785 mayeach include a conductive material, such as Al, Au, Pt, Ag, Ni, Ti, Cu,or any combination thereof (e.g., Ag/Pt/Au or Al/Ni/Au), and may act asthe electrodes of LED 705. In the example shown in FIG. 7B, electricalcontact 785 may be an n-contact, and electrical contact 765 may be ap-contact. Electrical contact 765 and semiconductor layer 745 (e.g., ap-type semiconductor layer) may form a back reflector for reflectinglight emitted by active layer 735 back toward substrate 715. In someembodiments, electrical contact 765 and metal layer 795 include samematerial(s) and can be formed using the same processes. In someembodiments, an additional conductive layer (not shown) may be includedas an intermediate conductive layer between the electrical contacts 765and 785 and the semiconductor layers.

When a voltage signal is applied across contacts 765 and 785, electronsand holes may recombine in active layer 735. The recombination ofelectrons and holes may cause photon emission, thus producing light. Thewavelength and energy of the emitted photons may depend on the energybandgap between the valence band and the conduction band in active layer735. For example, InGaN active layers may emit green or blue light,while AlInGaP active layers may emit red, orange, yellow, or greenlight. The emitted photons may propagate in many different directions,and may be reflected by the mesa reflector and/or the back reflector andmay exit LED 705, for example, from the bottom side (e.g., substrate715) shown in FIG. 7B. One or more other secondary optical components,such as a lens or a grating, may be formed on the light emissionsurface, such as substrate 715, to focus or collimate the emitted lightand/or couple the emitted light into a waveguide.

One or two-dimensional arrays of the LEDs described above may bemanufactured on a wafer to form light sources (e.g., light source 642).Driver circuits (e.g., driver circuit 644) may be fabricated, forexample, on a silicon wafer using CMOS processes. The LEDs and thedriver circuits on wafers may be diced and then bonded together, or maybe bonded on the wafer level and then diced. Various bonding techniquescan be used for bonding the LEDs and the driver circuits, such asadhesive bonding, metal-to-metal bonding, metal oxide bonding,wafer-to-wafer bonding, die-to-wafer bonding, hybrid bonding, and thelike.

FIG. 8A illustrates an example of a method of die-to-wafer bonding forarrays of LEDs according to certain embodiments. In the example shown inFIG. 8A, an LED array 801 may include a plurality of LEDs 807 on acarrier substrate 805. Carrier substrate 805 may include variousmaterials, such as GaAs, InP, GaN, MN, sapphire, SiC, Si, or the like.LEDs 807 may be fabricated by, for example, growing various epitaxiallayers, forming mesa structures, and forming electrical contacts orelectrodes, before performing the bonding. The epitaxial layers mayinclude various materials, such as GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP,(AlGaIn)AsN, (AlGaIn)Pas, (Eu:InGa)N, (AlGaIn)N, or the like, and mayinclude an n-type layer, a p-type layer, and an active layer thatincludes one or more heterostructures, such as one or more quantum wellsor MQWs. The electrical contacts may include various conductivematerials, such as a metal or a metal alloy.

A wafer 803 may include a base layer 809 having passive or activeintegrated circuits (e.g., driver circuits 811) fabricated thereon. Baselayer 809 may include, for example, a silicon wafer. Driver circuits 811may be used to control the operations of LEDs 807. For example, thedriver circuit for each LED 807 may include a 2T1C pixel structure thathas two transistors and one capacitor. Wafer 803 may also include abonding layer 813. Bonding layer 813 may include various materials, suchas a metal, an oxide, a dielectric, CuSn, AuTi, and the like. In someembodiments, a patterned layer 815 may be formed on a surface of bondinglayer 813, where patterned layer 815 may include a metallic grid made ofa conductive material, such as Cu, Ag, Au, Al, or the like.

LED array 801 may be bonded to wafer 803 via bonding layer 813 orpatterned layer 815. For example, patterned layer 815 may include metalpads or bumps made of various materials, such as CuSn, AuSn, ornanoporous Au, that may be used to align LEDs 807 of LED array 801 withcorresponding driver circuits 811 on wafer 803. In one example, LEDarray 801 may be brought toward wafer 803 until LEDs 807 come intocontact with respective metal pads or bumps corresponding to drivercircuits 811. Some or all of LEDs 807 may be aligned with drivercircuits 811, and may then be bonded to wafer 803 via patterned layer815 by various bonding techniques, such as metal-to-metal bonding. AfterLEDs 807 have been bonded to wafer 803, carrier substrate 805 may beremoved from LEDs 807.

FIG. 8B illustrates an example of a method of wafer-to-wafer bonding forarrays of LEDs according to certain embodiments. As shown in FIG. 8B, afirst wafer 802 may include a substrate 804, a first semiconductor layer806, active layers 808, and a second semiconductor layer 810. Substrate804 may include various materials, such as GaAs, InP, GaN, AlN,sapphire, SiC, Si, or the like. First semiconductor layer 806, activelayers 808, and second semiconductor layer 810 may include varioussemiconductor materials, such as GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP,(AlGaIn)AsN, (AlGaIn)Pas, (Eu:InGa)N, (AlGaIn)N, or the like. In someembodiments, first semiconductor layer 806 may be an n-type layer, andsecond semiconductor layer 810 may be a p-type layer. For example, firstsemiconductor layer 806 may be an n-doped GaN layer (e.g., doped with Sior Ge), and second semiconductor layer 810 may be a p-doped GaN layer(e.g., doped with Mg, Ca, Zn, or Be). Active layers 808 may include, forexample, one or more GaN layers, one or more InGaN layers, one or moreAlInGaP layers, and the like, which may form one or moreheterostructures, such as one or more quantum wells or MQWs.

In some embodiments, first wafer 802 may also include a bonding layer.Bonding layer 812 may include various materials, such as a metal, anoxide, a dielectric, CuSn, AuTi, or the like. In one example, bondinglayer 812 may include p-contacts and/or n-contacts (not shown). In someembodiments, other layers may also be included on first wafer 802, suchas a buffer layer between substrate 804 and first semiconductor layer806. The buffer layer may include various materials, such aspolycrystalline GaN or AlN. In some embodiments, a contact layer may bebetween second semiconductor layer 810 and bonding layer 812. Thecontact layer may include any suitable material for providing anelectrical contact to second semiconductor layer 810 and/or firstsemiconductor layer 806.

First wafer 802 may be bonded to wafer 803 that includes driver circuits811 and bonding layer 813 as described above, via bonding layer 813and/or bonding layer 812. Bonding layer 812 and bonding layer 813 may bemade of the same material or different materials. Bonding layer 813 andbonding layer 812 may be substantially flat. First wafer 802 may bebonded to wafer 803 by various methods, such as metal-to-metal bonding,eutectic bonding, metal oxide bonding, anodic bonding,thermo-compression bonding, ultraviolet (UV) bonding, and/or fusionbonding.

As shown in FIG. 8B, first wafer 802 may be bonded to wafer 803 with thep-side (e.g., second semiconductor layer 810) of first wafer 802 facingdown (i.e., toward wafer 803). After bonding, substrate 804 may beremoved from first wafer 802, and first wafer 802 may then be processedfrom the n-side. The processing may include, for example, the formationof certain mesa shapes for individual LEDs, as well as the formation ofoptical components corresponding to the individual LEDs.

FIGS. 9A-9D illustrate an example of a method of hybrid bonding forarrays of LEDs according to certain embodiments. The hybrid bonding maygenerally include wafer cleaning and activation, high-precisionalignment of contacts of one wafer with contacts of another wafer,dielectric bonding of dielectric materials at the surfaces of the wafersat room temperature, and metal bonding of the contacts by annealing atelevated temperatures. FIG. 9A shows a substrate 910 with passive oractive circuits 920 manufactured thereon. As described above withrespect to FIGS. 8A-8B, substrate 910 may include, for example, asilicon wafer. Circuits 920 may include driver circuits for the arraysof LEDs. A bonding layer may include dielectric regions 940 and contactpads 930 connected to circuits 920 through electrical interconnects 922.Contact pads 930 may include, for example, Cu, Ag, Au, Al, W, Mo, Ni,Ti, Pt, Pd, or the like. Dielectric materials in dielectric regions 940may include SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thebonding layer may be planarized and polished using, for example,chemical mechanical polishing, where the planarization or polishing maycause dishing (a bowl like profile) in the contact pads. The surfaces ofthe bonding layers may be cleaned and activated by, for example, an ion(e.g., plasma) or fast atom (e.g., Ar) beam 905. The activated surfacemay be atomically clean and may be reactive for formation of directbonds between wafers when they are brought into contact, for example, atroom temperature.

FIG. 9B illustrates a wafer 950 including an array of micro-LEDs 970fabricated thereon as described above with respect to, for example,FIGS. 7A-8B. Wafer 950 may be a carrier wafer and may include, forexample, GaAs, InP, GaN, AlN, sapphire, SiC, Si, or the like. Micro-LEDs970 may include an n-type layer, an active region, and a p-type layerepitaxially grown on wafer 950. The epitaxial layers may include variousIII-V semiconductor materials described above, and may be processed fromthe p-type layer side to etch mesa structures in the epitaxial layers,such as substantially vertical structures, parabolic structures, conicstructures, or the like. Passivation layers and/or reflection layers maybe formed on the sidewalls of the mesa structures. P-contacts 980 andn-contacts 982 may be formed in a dielectric material layer 960deposited on the mesa structures and may make electrical contacts withthe p-type layer and the n-type layers, respectively. Dielectricmaterials in dielectric material layer 960 may include, for example,SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. P-contacts 980and n-contacts 982 may include, for example, Cu, Ag, Au, Al, W, Mo, Ni,Ti, Pt, Pd, or the like. The top surfaces of p-contacts 980, n-contacts982, and dielectric material layer 960 may form a bonding layer. Thebonding layer may be planarized and polished using, for example,chemical mechanical polishing, where the polishing may cause dishing inp-contacts 980 and n-contacts 982. The bonding layer may then be cleanedand activated by, for example, an ion (e.g., plasma) or fast atom (e.g.,Ar) beam 915. The activated surface may be atomically clean and reactivefor formation of direct bonds between wafers when they are brought intocontact, for example, at room temperature.

FIG. 9C illustrates a room temperature bonding process for bonding thedielectric materials in the bonding layers. For example, after thebonding layer that includes dielectric regions 940 and contact pads 930and the bonding layer that includes p-contacts 980, n-contacts 982, anddielectric material layer 960 are surface activated, wafer 950 andmicro-LEDs 970 may be turned upside down and brought into contact withsubstrate 910 and the circuits formed thereon. In some embodiments,compression pressure 925 may be applied to substrate 910 and wafer 950such that the bonding layers are pressed against each other. Due to thesurface activation and the dishing in the contacts, dielectric regions940 and dielectric material layer 960 may be in direct contact becauseof the surface attractive force, and may react and form chemical bondsbetween them because the surface atoms may have dangling bonds and maybe in unstable energy states after the activation. Thus, the dielectricmaterials in dielectric regions 940 and dielectric material layer 960may be bonded together with or without heat treatment or pressure.

FIG. 9D illustrates an annealing process for bonding the contacts in thebonding layers after bonding the dielectric materials in the bondinglayers. For example, contact pads 930 and p-contacts 980 or n-contacts982 may be bonded together by annealing at, for example, about 200-400°C. or higher. During the annealing process, heat 935 may cause thecontacts to expand more than the dielectric materials (due to differentcoefficients of thermal expansion), and thus may close the dishing gapsbetween the contacts such that contact pads 930 and p-contacts 980 orn-contacts 982 may be in contact and may form direct metallic bonds atthe activated surfaces.

In some embodiments where the two bonded wafers include materials havingdifferent thermal expansion coefficients (TECs), the dielectricmaterials bonded at room temperature may help to reduce or preventmisalignment of the contact pads caused by the different thermalexpansions. In some embodiments, to further reduce or avoid themisalignment of the contact pads at a high temperature during annealing,trenches may be formed between micro-LEDs, between groups of micro-LEDs,through part or all of the substrate, or the like, before bonding.

After the micro-LEDs are bonded to the driver circuits, the substrate onwhich the micro-LEDs are fabricated may be thinned or removed, andvarious secondary optical components may be fabricated on the lightemitting surfaces of the micro-LEDs to, for example, extract, collimate,and redirect the light emitted from the active regions of themicro-LEDs. In one example, micro-lenses may be formed on themicro-LEDs, where each micro-lens may correspond to a respectivemicro-LED and may help to improve the light extraction efficiency andcollimate the light emitted by the micro-LED. In some embodiments, thesecondary optical components may be fabricated in the substrate or then-type layer of the micro-LEDs. In some embodiments, the secondaryoptical components may be fabricated in a dielectric layer deposited onthe n-type side of the micro-LEDs. Examples of the secondary opticalcomponents may include a lens, a grating, an antireflection (AR)coating, a prism, a photonic crystal, or the like.

FIG. 10 illustrates an example of an LED array 1000 with secondaryoptical components fabricated thereon according to certain embodiments.LED array 1000 may be made by bonding an LED chip or wafer with asilicon wafer including electrical circuits fabricated thereon, usingany suitable bonding techniques described above with respect to, forexample, FIGS. 8A-9D. In the example shown in FIG. 10 , LED array 1000may be bonded using a wafer-to-wafer hybrid bonding technique asdescribed above with respect to FIG. 9A-9D. LED array 1000 may include asubstrate 1010, which may be, for example, a silicon wafer. Integratedcircuits 1020, such as LED driver circuits, may be fabricated onsubstrate 1010. Integrated circuits 1020 may be connected to p-contacts1074 and n-contacts 1072 of micro-LEDs 1070 through interconnects 1022and contact pads 1030, where contact pads 1030 may form metallic bondswith p-contacts 1074 and n-contacts 1072. Dielectric layer 1040 onsubstrate 1010 may be bonded to dielectric layer 1060 through fusionbonding.

The substrate (not shown) of the LED chip or wafer may be thinned or maybe removed to expose the n-type layer 1050 of micro-LEDs 1070. Varioussecondary optical components, such as a spherical micro-lens 1082, agrating 1084, a micro-lens 1086, an antireflection layer 1088, and thelike, may be formed in or on top of n-type layer 1050. For example,spherical micro-lens arrays may be etched in the semiconductor materialsof micro-LEDs 1070 using a gray-scale mask and a photoresist with alinear response to exposure light, or using an etch mask formed bythermal reflowing of a patterned photoresist layer. The secondaryoptical components may also be etched in a dielectric layer deposited onn-type layer 1050 using similar photolithographic techniques or othertechniques. For example, micro-lens arrays may be formed in a polymerlayer through thermal reflowing of the polymer layer that is patternedusing a binary mask. The micro-lens arrays in the polymer layer may beused as the secondary optical components or may be used as the etch maskfor transferring the profiles of the micro-lens arrays into a dielectriclayer or a semiconductor layer. The dielectric layer may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. In someembodiments, a micro-LED 1070 may have multiple corresponding secondaryoptical components, such as a micro-lens and an anti-reflection coating,a micro-lens etched in the semiconductor material and a micro-lensetched in a dielectric material layer, a micro-lens and a grating, aspherical lens and an aspherical lens, and the like. Three differentsecondary optical components are illustrated in FIG. 10 to show someexamples of secondary optical components that can be formed onmicro-LEDs 1070, which does not necessary imply that different secondaryoptical components are used simultaneously for every LED array.

FIG. 11A illustrates an example of an LED array 1100 that may be formedaccording to the hybrid bonding method described above with respect toFIGS. 9A-9D, and that may have LEDs with vertical and parabolic mesashapes. The LED array 1100 may include a one-dimensional array of LEDsor a two-dimensional array of LEDs. Each LED of the LED array may be alarge LED, a mini LED, a micro-LED, a tapered LED, or a superluminescentdiode (SLED). In other embodiments, lasers may be used in place of theLEDs. Each LED of the LED array 1100 may include a semiconductor layerstack that has an n-side semiconductor layer 1112, an active lightemitting layer 1114, and a p-side semiconductor layer 1116. Thesemiconductor layer stack may include a III-V material, such as GaN,InGaN, (AlGaIn)P, (AlGaIn)AsP, (AlGaIn)AsN, (AlGaIn)PAs, (Eu:InGa)N, or(AlGaIn)N. The n-side semiconductor layer 1112 may be n-doped (e.g.,with Si or Ge) and the p-side semiconductor layer 1116 may be p-doped(e.g., with Mg, Ca, Zn, or Be). The semiconductor layer stack may have athickness of less than 2 μm. The active light emitting layer 1114 may besandwiched between the n-side semiconductor layer 1112 and the p-sidesemiconductor layer 1116, and may include one or more InGaN layers, oneor more AlInGaP layers, and/or one or more GaN layers, which may formone or more heterostructures, such as one or more quantum wells or MQWs.A first LED 1144 1144 may have a vertical mesa shape, and a second LED1146 may have a parabolic mesa shape. Although the first LED 1144 andthe second LED 1146 are shown as having different mesa shapes, some orall of the LEDs within the LED array 1100 may have the same mesa shape.A substrate 1110 may be a growth substrate for the LEDs or a temporarybond wafer.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1118. For example, for a red LED, the highly p-doped layer1118 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1118 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1116. P-contacts 1120 may be provided beneath thesemiconductor layer stack. The p-contacts 1120 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1118 may be optimized for making contact to the p-contacts 1120.In addition, a dielectric layer 1132 may be formed around a reflectorlayer 1130 of each of the LEDs. The dielectric layer 1132 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1130 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1130 may reflect light that isemitted by the active light emitting layer 1114. Further, each reflectorlayer 1130 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1112. Due to the configuration of then-side semiconductor layer 1112, the first LED 1144 may have an isolatedn-contact, while the second LED 1146 and a third LED 1148 may have acommon n-contact. The p-contacts 1120 and/or the reflector layer 1130may form a pattern of metal tracks through the dielectric layer 1132.The bottom surfaces of the p-contacts 1120 and the reflector layer 1130may be recessed with respect to the bottom surface of the dielectriclayer 1132. A thermal expansion coefficient of the p-contacts 1120and/or the reflector layer 1130 may be higher than a thermal expansioncoefficient of the dielectric layer 1132.

The LEDs may be bonded to a substrate 1128 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1128 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1128 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1124may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1128. Similarly,n-contacts 1126 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1128.The p-contacts 1124 and the n-contacts 1126 may be configured to drivethe LEDs. The p-contacts 1124 and the n-contacts 1126 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1122 may be formed between the p-contacts1124 and the n-contacts 1126. The dielectric layer 1122 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1124 and/or the n-contacts 1126 may form a pattern of metaltracks through the dielectric layer 1122. The top surface of thedielectric layer 1122 may be recessed with respect to the top surfacesof the p-contacts 1124 and/or the n-contacts 1126. A thermal expansioncoefficient of the p-contacts 1124 and/or the n-contacts 1126 may behigher than a thermal expansion coefficient of the dielectric layer1122.

Before bonding the LEDs to the substrate 1128, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1124, the n-contacts 1126,and/or the dielectric layer 1122 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1120, the reflector layer 1130, and/or the dielectric layer 1132 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1120 may be aligned with p-contacts 1124. For example, thepattern of metal tracks formed by the p-contacts 1120 through thedielectric layer 1132 may be aligned with the pattern of metal tracksformed by the p-contacts 1124 through the dielectric layer 1122. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1132 with the dielectric layer 1122, and thenperforming metal bonding of p-contacts 1120 with p-contacts 1124. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1132 and the dielectric layer 1122. The dielectriclayer 1132 and the dielectric layer 1122 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1132 and/or thedielectric layer 1122 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1100 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1120 and the p-contacts 1124. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1120 and the p-contacts 1124.

Alternatively or in addition, reflector layers 1130 may be aligned withn-contacts 1126. For example, the pattern of metal tracks formed by thereflector layers 1130 through the dielectric layer 1132 may be alignedwith the pattern of metal tracks formed by the n-contacts 1126 throughthe dielectric layer 1122. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1132 with thedielectric layer 1122, and then performing metal bonding of reflectorlayers 1130 with n-contacts 1126. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1132 and thedielectric layer 1122. The dielectric layer 1132 and the dielectriclayer 1122 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1132 and/or the dielectric layer 1122 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1100 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1130 and the n-contacts1126. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1130 and then-contacts 1126.

FIG. 11B illustrates an example of another LED array 1105 that may beformed according to the hybrid bonding method described above withrespect to FIGS. 9A-9D, and that may have LEDs with vertical and conicalmesa shapes. The LED array 1105 may include a one-dimensional array ofLEDs or a two-dimensional array of LEDs. Each LED of the LED array maybe a large LED, a mini LED, a micro-LED, a tapered LED, or asuperluminescent diode (SLED). In other embodiments, lasers may be usedin place of the LEDs. Each LED of the LED array 1105 may include asemiconductor layer stack that has an n-side semiconductor layer 1152,an active light emitting layer 1154, and a p-side semiconductor layer1156. The semiconductor layer stack may include a III-V material, suchas GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP, (AlGaIn)AsN, (AlGaIn)PAs,(Eu:InGa)N, or (AlGaIn)N. The n-side semiconductor layer 1152 may ben-doped (e.g., with Si or Ge) and the p-side semiconductor layer 1156may be p-doped (e.g., with Mg, Ca, Zn, or Be). The semiconductor layerstack may have a thickness of less than 2 μm. The active light emittinglayer 1154 may be sandwiched between the n-side semiconductor layer 1152and the p-side semiconductor layer 1156, and may include one or moreInGaN layers, one or more AlInGaP layers, and/or one or more GaN layers,which may form one or more heterostructures, such as one or more quantumwells or MQWs. A first LED 1184 may have a vertical mesa shape, and asecond LED 1186 may have a conical mesa shape. Although the first LED1184 and the second LED 1186 are shown as having different mesa shapes,some or all of the LEDs within the LED array 1105 may have the same mesashape. A substrate 1150 may be a growth substrate for the LEDs or atemporary bond wafer.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1158. For example, for a red LED, the highly p-doped layer1158 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1158 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1156. P-contacts 1160 may be provided beneath thesemiconductor layer stack. The p-contacts 1160 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1158 may be optimized for making contact to the p-contacts 1160.In addition, a dielectric layer 1172 may be formed around a reflectorlayer 1170 of each of the LEDs. The dielectric layer 1172 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1170 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1170 may reflect light that isemitted by the active light emitting layer 1154. Further, each reflectorlayer 1170 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1152. Due to the configuration of then-side semiconductor layer 1152, the first LED 1184 may have an isolatedn-contact, while the second LED 1186 and a third LED 1188 may have acommon n-contact. The p-contacts 1160 and/or the reflector layer 1170may form a pattern of metal tracks through the dielectric layer 1172.The bottom surfaces of the p-contacts 1160 and the reflector layer 1170may be recessed with respect to the bottom surface of the dielectriclayer 1172. A thermal expansion coefficient of the p-contacts 1160and/or the reflector layer 1170 may be higher than a thermal expansioncoefficient of the dielectric layer 1172.

The LEDs may be bonded to a substrate 1168 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1168 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1168 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1164may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1168. Similarly,n-contacts 1166 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1168.The p-contacts 1164 and the n-contacts 1166 may be configured to drivethe LEDs. The p-contacts 1164 and the n-contacts 1166 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1162 may be formed between the p-contacts1164 and the n-contacts 1166. The dielectric layer 1162 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1164 and/or the n-contacts 1166 may form a pattern of metaltracks through the dielectric layer 1162. The top surface of thedielectric layer 1162 may be recessed with respect to the top surfacesof the p-contacts 1164 and/or the n-contacts 1166. A thermal expansioncoefficient of the p-contacts 1164 and/or the n-contacts 1166 may behigher than a thermal expansion coefficient of the dielectric layer1162.

Before bonding the LEDs to the substrate 1168, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1164, the n-contacts 1166,and/or the dielectric layer 1162 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1160, the reflector layer 1170, and/or the dielectric layer 1172 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1160 may be aligned with p-contacts 1164. For example, thepattern of metal tracks formed by the p-contacts 1160 through thedielectric layer 1172 may be aligned with the pattern of metal tracksformed by the p-contacts 1164 through the dielectric layer 1162. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1172 with the dielectric layer 1162, and thenperforming metal bonding of p-contacts 1160 with p-contacts 1164. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1172 and the dielectric layer 1162. The dielectriclayer 1172 and the dielectric layer 1162 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1172 and/or thedielectric layer 1162 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1105 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1160 and the p-contacts 1164. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1160 and the p-contacts 1164.

Alternatively or in addition, reflector layers 1170 may be aligned withn-contacts 1166. For example, the pattern of metal tracks formed by thereflector layers 1170 through the dielectric layer 1172 may be alignedwith the pattern of metal tracks formed by the n-contacts 1166 throughthe dielectric layer 1162. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1172 with thedielectric layer 1162, and then performing metal bonding of reflectorlayers 1170 with n-contacts 1166. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1172 and thedielectric layer 1162. The dielectric layer 1172 and the dielectriclayer 1162 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1172 and/or the dielectric layer 1162 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1105 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1170 and the n-contacts1166. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1170 and then-contacts 1166.

FIG. 12A illustrates an example of an LED array 1200 that may be formedaccording to the hybrid bonding method described above with respect toFIGS. 9A-9D, and that may undergo n-side processing. The LED array 1200may include a one-dimensional array of LEDs or a two-dimensional arrayof LEDs. Each LED of the LED array may be a large LED, a mini LED, amicro-LED, a tapered LED, or a superluminescent diode (SLED). In otherembodiments, lasers may be used in place of the LEDs. Each LED of theLED array 1200 may include a semiconductor layer stack that has ann-side semiconductor layer 1212, an active light emitting layer 1214,and a p-side semiconductor layer 1216. The semiconductor layer stack mayinclude a III-V material, such as GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP,(AlGaIn)AsN, (AlGaIn)PAs, (Eu:InGa)N, or (AlGaIn)N. The n-sidesemiconductor layer 1212 may be n-doped (e.g., with Si or Ge) and thep-side semiconductor layer 1216 may be p-doped (e.g., with Mg, Ca, Zn,or Be). The semiconductor layer stack may have a thickness of less than2 μm. The active light emitting layer 1214 may be sandwiched between then-side semiconductor layer 1212 and the p-side semiconductor layer 1216,and may include one or more InGaN layers, one or more AlInGaP layers,and/or one or more GaN layers, which may form one or moreheterostructures, such as one or more quantum wells or MQWs. A first LED1244 may have a vertical mesa shape, and a second LED 1246 may have aparabolic mesa shape. Although the first LED 1244 and the second LED1246 are shown as having different mesa shapes, some or all of the LEDswithin the LED array 1200 may have the same mesa shape. A substrate 1210may be a growth substrate for the LEDs or a temporary bond wafer.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1218. For example, for a red LED, the highly p-doped layer1218 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1218 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1116. P-contacts 1220 may be provided beneath thesemiconductor layer stack. The p-contacts 1220 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1218 may be optimized for making contact to the p-contacts 1220.In addition, a dielectric layer 1232 may be formed around a reflectorlayer 1230 of each of the LEDs. The dielectric layer 1232 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1230 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1230 may reflect light that isemitted by the active light emitting layer 1214. Further, each reflectorlayer 1230 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1212. Due to the configuration of then-side semiconductor layer 1212, the first LED 1244 may have an isolatedn-contact, while the second LED 1246 and a third LED 1248 may have acommon n-contact. The p-contacts 1220 and/or the reflector layer 1230may form a pattern of metal tracks through the dielectric layer 1232.The bottom surfaces of the p-contacts 1220 and the reflector layer 1230may be recessed with respect to the bottom surface of the dielectriclayer 1232. A thermal expansion coefficient of the p-contacts 1220and/or the reflector layer 1230 may be higher than a thermal expansioncoefficient of the dielectric layer 1232.

The LEDs may be bonded to a substrate 1228 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1228 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1228 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1224may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1228. Similarly,n-contacts 1226 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1228.The p-contacts 1224 and the n-contacts 1226 may be configured to drivethe LEDs. The p-contacts 1224 and the n-contacts 1226 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1222 may be formed between the p-contacts1224 and the n-contacts 1226. The dielectric layer 1222 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1224 and/or the n-contacts 1226 may form a pattern of metaltracks through the dielectric layer 1222. The top surface of thedielectric layer 1222 may be recessed with respect to the top surfacesof the p-contacts 1224 and/or the n-contacts 1226. A thermal expansioncoefficient of the p-contacts 1224 and/or the n-contacts 1226 may behigher than a thermal expansion coefficient of the dielectric layer1222.

Before bonding the LEDs to the substrate 1228, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1224, the n-contacts 1226,and/or the dielectric layer 1222 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1220, the reflector layer 1230, and/or the dielectric layer 1232 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1220 may be aligned with p-contacts 1224. For example, thepattern of metal tracks formed by the p-contacts 1220 through thedielectric layer 1232 may be aligned with the pattern of metal tracksformed by the p-contacts 1224 through the dielectric layer 1222. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1232 with the dielectric layer 1222, and thenperforming metal bonding of p-contacts 1220 with p-contacts 1224. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1232 and the dielectric layer 1222. The dielectriclayer 1232 and the dielectric layer 1222 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1232 and/or thedielectric layer 1222 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1200 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1220 and the p-contacts 1224. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1220 and the p-contacts 1224.

Alternatively or in addition, reflector layers 1230 may be aligned withn-contacts 1226. For example, the pattern of metal tracks formed by thereflector layers 1230 through the dielectric layer 1232 may be alignedwith the pattern of metal tracks formed by the n-contacts 1226 throughthe dielectric layer 1222. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1232 with thedielectric layer 1222, and then performing metal bonding of reflectorlayers 1230 with n-contacts 1226. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1232 and thedielectric layer 1222. The dielectric layer 1232 and the dielectriclayer 1222 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1232 and/or the dielectric layer 1222 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1200 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1230 and the n-contacts1226. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1230 and then-contacts 1226.

FIG. 12B illustrates an example of another LED array 1205 that may beformed according to the hybrid bonding method described above withrespect to FIGS. 9A-9D, and that may undergo p-side processing. The LEDarray 1205 may include a one-dimensional array of LEDs or atwo-dimensional array of LEDs. Each LED of the LED array may be a largeLED, a mini LED, a micro-LED, a tapered LED, or a superluminescent diode(SLED). In other embodiments, lasers may be used in place of the LEDs.Each LED of the LED array 1205 may include a semiconductor layer stackthat has an n-side semiconductor layer 1252, an active light emittinglayer 1254, and a p-side semiconductor layer 1256. The semiconductorlayer stack may include a III-V material, such as GaN, InGaN, (AlGaIn)P,(AlGaIn)AsP, (AlGaIn)AsN, (AlGaIn)PAs, (Eu:InGa)N, or (AlGaIn)N. Then-side semiconductor layer 1252 may be n-doped (e.g., with Si or Ge) andthe p-side semiconductor layer 1256 may be p-doped (e.g., with Mg, Ca,Zn, or Be). The semiconductor layer stack may have a thickness of lessthan 2 μm. The active light emitting layer 1254 may be sandwichedbetween the n-side semiconductor layer 1252 and the p-side semiconductorlayer 1256, and may include one or more InGaN layers, one or moreAlInGaP layers, and/or one or more GaN layers, which may form one ormore heterostructures, such as one or more quantum wells or MQWs. Afirst LED 1284 may have a vertical mesa shape, and a second LED 1286 mayhave a parabolic mesa shape. Although the first LED 1284 and the secondLED 1286 are shown as having different mesa shapes, some or all of theLEDs within the LED array may have the same mesa shape. A substrate 1250may be a growth substrate for the LEDs or a temporary bond wafer.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1258. For example, for a red LED, the highly p-doped layer1258 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1258 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1256. P-contacts 1260 may be provided beneath thesemiconductor layer stack. The p-contacts 1260 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1258 may be optimized for making contact to the p-contacts 1260.In addition, a dielectric layer 1272 may be formed around a reflectorlayer 1270 of each of the LEDs. The dielectric layer 1272 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1270 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1270 may reflect light that isemitted by the active light emitting layer 1254. Further, each reflectorlayer 1270 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1252. Due to the configuration of then-side semiconductor layer 1252, the first LED 1284 may have an isolatedn-contact, while the second LED 1286 and a third LED 1288 may have acommon n-contact. The p-contacts 1260 and/or the reflector layer 1270may form a pattern of metal tracks through the dielectric layer 1272.The bottom surfaces of the p-contacts 1260 and the reflector layer 1270may be recessed with respect to the bottom surface of the dielectriclayer 1272. A thermal expansion coefficient of the p-contacts 1260and/or the reflector layer 1270 may be higher than a thermal expansioncoefficient of the dielectric layer 1272.

The LEDs may be bonded to a substrate 1268 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1268 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1268 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1264may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1268. Similarly,n-contacts 1266 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1268.The p-contacts 1264 and the n-contacts 1266 may be configured to drivethe LEDs. The p-contacts 1264 and the n-contacts 1266 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1262 may be formed between the p-contacts1264 and the n-contacts 1266. The dielectric layer 1262 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1264 and/or the n-contacts 1266 may form a pattern of metaltracks through the dielectric layer 1262. The top surface of thedielectric layer 1262 may be recessed with respect to the top surfacesof the p-contacts 1264 and/or the n-contacts 1266. A thermal expansioncoefficient of the p-contacts 1264 and/or the n-contacts 1266 may behigher than a thermal expansion coefficient of the dielectric layer1262.

Before bonding the LEDs to the substrate 1268, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1264, the n-contacts 1266,and/or the dielectric layer 1262 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1260, the reflector layer 1270, and/or the dielectric layer 1272 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1260 may be aligned with p-contacts 1264. For example, thepattern of metal tracks formed by the p-contacts 1260 through thedielectric layer 1272 may be aligned with the pattern of metal tracksformed by the p-contacts 1264 through the dielectric layer 1262. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1272 with the dielectric layer 1262, and thenperforming metal bonding of p-contacts 1260 with p-contacts 1264. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1272 and the dielectric layer 1262. The dielectriclayer 1272 and the dielectric layer 1262 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1272 and/or thedielectric layer 1262 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1205 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1260 and the p-contacts 1264. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1260 and the p-contacts 1264.

Alternatively or in addition, reflector layers 1270 may be aligned withn-contacts 1266. For example, the pattern of metal tracks formed by thereflector layers 1270 through the dielectric layer 1272 may be alignedwith the pattern of metal tracks formed by the n-contacts 1266 throughthe dielectric layer 1262. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1272 with thedielectric layer 1262, and then performing metal bonding of reflectorlayers 1270 with n-contacts 1266. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1272 and thedielectric layer 1262. The dielectric layer 1272 and the dielectriclayer 1262 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1272 and/or the dielectric layer 1262 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1205 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1270 and the n-contacts1266. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1270 and then-contacts 1266.

One advantage of the hybrid bonding method described with reference toFIGS. 9A-9D is that the LED array can be processed from both the n-sideand the p-side. For example, before performing hybrid bonding, the LEDarray may be processed from a direction adjacent to the p-sidesemiconductor layer. This direction is generally indicated by the ion orfast atom beam 915 shown in FIG. 9B. The p-side processing may occurfrom above along a direction that is perpendicular to a plane that isparallel to a top surface of the n-contacts 982, the p-contacts 980,and/or the dielectric material layer 960. Alternatively, the p-sideprocessing may occur from above along a direction having an angle ofless than 90° with respect to the perpendicular direction. Referring toFIG. 12B, the p-side processing 1278 may occur from below along adirection that is perpendicular to a plane that is parallel to a bottomsurface of the p-contacts 1260 and/or the dielectric layer 1272.Alternatively, the p-side processing 1278 may occur from below along adirection having an angle of less than 90° with respect to theperpendicular direction. Put another way, the p-side processing 1278 mayoccur from below along a direction that is adjacent to the bottomsurface of the p-side semiconductor layer 1256, which is opposite to theactive light emitting layer 1254.

Various types of p-side processing 1278 may be performed. For example,the p-side processing 1278 may include forming a plurality of mesashapes within the p-side semiconductor layer 1256, the active lightemitting layer 1254, and the n-side semiconductor layer 1252. Forexample, the first LED 1284 has a vertical mesa shape, and the secondLED 1286 has a parabolic mesa shape. Within an LED array, the pluralityof LEDs may have the same mesa shape or different mesa shapes. Thep-side processing 1278 may also include forming a reflective layer onone, some, or all of the plurality of mesa shapes, such as the reflectorlayer 1270 shown in FIG. 12B. In some examples, the reflector layer 1270may have a reflectivity that is greater than 80%.

Alternatively or in addition, the p-side processing 1278 may includeperforming ion implantation to increase the light output power (LOP) anddecrease carrier leakage at low currents. Ion implantation is discussedin further detail below with respect to FIGS. 32-35B. Alternatively orin addition, the p-side processing 1278 may include quantum wellintermixing to reduce lateral light reabsorption in the quantum wells,and to reduce lateral current flow and surface recombination losses atthe mesa facets. Quantum well intermixing is discussed in further detailbelow with respect to FIGS. 36A-36C.

Alternatively or in addition, the p-side processing 1278 may includeperforming atomic layer deposition (ALD) of the semiconductor layerstack. Alternatively or in addition, the p-side processing 1278 mayinclude performing overgrowth of the semiconductor layer stack. In someexamples, the overgrowth may be performed by using molecular beamepitaxy (MBE). The ALD and/or the MBE may reduce surface recombinationlosses at a mesa facet of the plurality of mesa shapes.

Alternatively or in addition, before or after performing hybrid bonding,the LED array may be processed from a direction adjacent to the n-sidesemiconductor layer. Referring to FIG. 12A, n-side processing 1238 mayoccur from above along a direction that is perpendicular to a plane thatis parallel to a top surface of the n-side semiconductor layer 1212.Alternatively, the n-side processing 1238 may occur from above along adirection having an angle of less than 90° with respect to theperpendicular direction. Put another way, the n-side processing 1238 mayoccur from above along a direction that is adjacent to the top surfaceof the n-side semiconductor layer 1212, which is opposite to the activelight emitting layer 1214.

Various types of n-side processing 1238 may be performed. For example,the n-side processing 1238 may include performing ion implantation toincrease the light output power (LOP) and decrease carrier leakage atlow currents. Ion implantation is discussed in further detail below withrespect to FIGS. 32-35B. Alternatively or in addition, the n-sideprocessing 1238 may include quantum well intermixing to reduce laterallight reabsorption in the quantum wells, and to reduce lateral currentflow and surface recombination losses at the mesa facets. Quantum wellintermixing is discussed in further detail below with respect to FIGS.36A-36C. Alternatively or in addition, the n-side processing 1238 mayinclude etch processes such as singulation of the arrays. Alternativelyor in addition, the n-side processing 1238 may include depositionprocesses to deposit lateral conductors such as indium tin oxide (ITO)and/or dielectric layers such as SiN or SiO for isolation or opticalpurposes.

FIG. 13A illustrates an example of another LED array 1300 that may beformed according to the hybrid bonding method described above withrespect to FIGS. 9A-9D, and that may include secondary optics such asmicro-lenses. The LED array 1300 may include a one-dimensional array ofLEDs or a two-dimensional array of LEDs. Each LED of the LED array maybe a large LED, a mini LED, a micro-LED, a tapered LED, or asuperluminescent diode (SLED). In other embodiments, lasers may be usedin place of the LEDs. Each LED of the LED array 1300 may include asemiconductor layer stack that has an n-side semiconductor layer 1312,an active light emitting layer 1314, and a p-side semiconductor layer1316. The semiconductor layer stack may include a III-V material, suchas GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP, (AlGaIn)AsN, (AlGaIn)PAs,(Eu:InGa)N, or (AlGaIn)N. The n-side semiconductor layer 1312 may ben-doped (e.g., with Si or Ge) and the p-side semiconductor layer 1316may be p-doped (e.g., with Mg, Ca, Zn, or Be). The semiconductor layerstack may have a thickness of less than 2 μm. The active light emittinglayer 1314 may be sandwiched between the n-side semiconductor layer 1312and the p-side semiconductor layer 1316, and may include one or moreInGaN layers, one or more AlInGaP layers, and/or one or more GaN layers,which may form one or more heterostructures, such as one or more quantumwells or MQWs. A first LED 1344 may have a vertical mesa shape, and asecond LED 1346 may have a parabolic mesa shape. Although the first LED1344 and the second LED 1346 are shown as having different mesa shapes,some or all of the LEDs within the LED array 1300 may have the same mesashape.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1318. For example, for a red LED, the highly p-doped layer1318 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1318 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1316. P-contacts 1320 may be provided beneath thesemiconductor layer stack. The p-contacts 1320 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1318 may be optimized for making contact to the p-contacts 1320.In addition, a dielectric layer 1332 may be formed around a reflectorlayer 1330 of each of the LEDs. The dielectric layer 1332 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1330 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1330 may reflect light that isemitted by the active light emitting layer 1314. Further, each reflectorlayer 1330 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1312. Due to the configuration of then-side semiconductor layer 1312, the first LED 1344 may have an isolatedn-contact, while the second LED 1346 and a third LED 1348 may have acommon n-contact. The p-contacts 1320 and/or the reflector layer 1330may form a pattern of metal tracks through the dielectric layer 1332.The bottom surfaces of the p-contacts 1320 and the reflector layer 1330may be recessed with respect to the bottom surface of the dielectriclayer 1332. A thermal expansion coefficient of the p-contacts 1320and/or the reflector layer 1330 may be higher than a thermal expansioncoefficient of the dielectric layer 1332.

The LEDs may be bonded to a substrate 1328 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1328 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1328 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1324may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1328. Similarly,n-contacts 1326 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1328.The p-contacts 1324 and the n-contacts 1326 may be configured to drivethe LEDs. The p-contacts 1324 and the n-contacts 1326 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1322 may be formed between the p-contacts1324 and the n-contacts 1326. The dielectric layer 1322 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1324 and/or the n-contacts 1326 may form a pattern of metaltracks through the dielectric layer 1322. The top surface of thedielectric layer 1322 may be recessed with respect to the top surfacesof the p-contacts 1324 and/or the n-contacts 1326. A thermal expansioncoefficient of the p-contacts 1324 and/or the n-contacts 1326 may behigher than a thermal expansion coefficient of the dielectric layer1322.

Before bonding the LEDs to the substrate 1328, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1324, the n-contacts 1326,and/or the dielectric layer 1322 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1320, the reflector layer 1330, and/or the dielectric layer 1332 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1320 may be aligned with p-contacts 1324. For example, thepattern of metal tracks formed by the p-contacts 1320 through thedielectric layer 1332 may be aligned with the pattern of metal tracksformed by the p-contacts 1324 through the dielectric layer 1322. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1332 with the dielectric layer 1322, and thenperforming metal bonding of p-contacts 1320 with p-contacts 1324. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1332 and the dielectric layer 1322. The dielectriclayer 1332 and the dielectric layer 1322 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1332 and/or thedielectric layer 1322 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1300 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1320 and the p-contacts 1324. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1320 and the p-contacts 1324.

Alternatively or in addition, reflector layers 1330 may be aligned withn-contacts 1326. For example, the pattern of metal tracks formed by thereflector layers 1330 through the dielectric layer 1332 may be alignedwith the pattern of metal tracks formed by the n-contacts 1326 throughthe dielectric layer 1322. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1332 with thedielectric layer 1322, and then performing metal bonding of reflectorlayers 1330 with n-contacts 1326. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1332 and thedielectric layer 1322. The dielectric layer 1332 and the dielectriclayer 1322 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1332 and/or the dielectric layer 1322 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1300 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1330 and the n-contacts1326. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1330 and then-contacts 1326.

FIG. 13B illustrates an example of another LED array 1305 that may beformed according to the hybrid bonding method described above withrespect to FIGS. 9A-9D, and that may include secondary optics such as ARcoatings and gratings. The LED array 1305 may include a one-dimensionalarray of LEDs or a two-dimensional array of LEDs. Each LED of the LEDarray may be a large LED, a mini LED, a micro-LED, a tapered LED, or asuperluminescent diode (SLED). In other embodiments, lasers may be usedin place of the LEDs. Each LED of the LED array 1305 may include asemiconductor layer stack that has an n-side semiconductor layer 1352,an active light emitting layer 1354, and a p-side semiconductor layer1356. The semiconductor layer stack may include a III-V material, suchas GaN, InGaN, (AlGaIn)P, (AlGaIn)AsP, (AlGaIn)AsN, (AlGaIn)PAs,(Eu:InGa)N, or (AlGaIn)N. The n-side semiconductor layer 1352 may ben-doped (e.g., with Si or Ge) and the p-side semiconductor layer 1356may be p-doped (e.g., with Mg, Ca, Zn, or Be). The semiconductor layerstack may have a thickness of less than 2 μm. The active light emittinglayer 1354 may be sandwiched between the n-side semiconductor layer 1352and the p-side semiconductor layer 1356, and may include one or moreInGaN layers, one or more AlInGaP layers, and/or one or more GaN layers,which may form one or more heterostructures, such as one or more quantumwells or MQWs. A first LED 1384 may have a vertical mesa shape, and asecond LED 1386 may have a parabolic mesa shape.

Optionally, the semiconductor layer stack may also include a highlyp-doped layer 1358. For example, for a red LED, the highly p-doped layer1358 may include highly p-doped GaP or AlGaAs. The highly p-doped layer1358 may have a higher concentration of p-type doping than the p-sidesemiconductor layer 1356. P-contacts 1360 may be provided beneath thesemiconductor layer stack. The p-contacts 1360 may include, for example,Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. The highly p-dopedlayer 1358 may be optimized for making contact to the p-contacts 1360.In addition, a dielectric layer 1372 may be formed around a reflectorlayer 1370 of each of the LEDs. The dielectric layer 1372 may include,for example, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like.Each reflector layer 1370 may include, for example, one or more metal ormetal alloy materials, such as Al, Ag, Au, Pt, Ti, Cu, or anycombination thereof. Each reflector layer 1370 may reflect light that isemitted by the active light emitting layer 1354. Further, each reflectorlayer 1370 may act as an n-contact by providing electrical contact tothe n-side semiconductor layer 1352. Due to the configuration of then-side semiconductor layer 1352, the first LED 1384 may have an isolatedn-contact, while the second LED 1386 and a third LED 1388 may have acommon n-contact. The p-contacts 1360 and/or the reflector layer 1370may form a pattern of metal tracks through the dielectric layer 1372.The bottom surfaces of the p-contacts 1360 and the reflector layer 1370may be recessed with respect to the bottom surface of the dielectriclayer 1372. A thermal expansion coefficient of the p-contacts 1360and/or the reflector layer 1370 may be higher than a thermal expansioncoefficient of the dielectric layer 1372.

The LEDs may be bonded to a substrate 1368 according to the hybridbonding method described above with respect to FIGS. 9A-9D. Thesubstrate 1368 may be a passive backplane or an active CMOSSi-backplane. For example, the substrate 1368 may include a passive oran active matrix integrated circuit within a Si layer. P-contacts 1364may provide electrical contact to certain passive or active circuits(not shown) within the Si layer of the substrate 1368. Similarly,n-contacts 1366 may provide electrical contact to other passive oractive circuits (not shown) within the Si layer of the substrate 1368.The p-contacts 1364 and the n-contacts 1366 may be configured to drivethe LEDs. The p-contacts 1364 and the n-contacts 1366 may include, forexample, Cu, Ag, Au, Al, W, Mo, Ni, Ti, Pt, Pd, or the like. Inaddition, a dielectric layer 1362 may be formed between the p-contacts1364 and the n-contacts 1366. The dielectric layer 1362 may include, forexample, SiCN, SiO₂, SiN, Al₂O₃, HfO₂, ZrO₂, Ta₂O₅, or the like. Thep-contacts 1364 and/or the n-contacts 1366 may form a pattern of metaltracks through the dielectric layer 1362. The top surface of thedielectric layer 1362 may be recessed with respect to the top surfacesof the p-contacts 1364 and/or the n-contacts 1366. A thermal expansioncoefficient of the p-contacts 1364 and/or the n-contacts 1366 may behigher than a thermal expansion coefficient of the dielectric layer1362.

Before bonding the LEDs to the substrate 1368, various bonding surfacesmay be planarized and polished using, for example, chemical mechanicalpolishing, as described above with reference to FIGS. 9A and 9B. Forexample, the top surfaces of the p-contacts 1364, the n-contacts 1366,and/or the dielectric layer 1362 may be planarized and polished.Alternatively or in addition, the bottom surfaces of the p-contacts1360, the reflector layer 1370, and/or the dielectric layer 1372 may beplanarized and polished. Some or all of the bonding surfaces may also becleaned and activated.

P-contacts 1360 may be aligned with p-contacts 1364. For example, thepattern of metal tracks formed by the p-contacts 1360 through thedielectric layer 1372 may be aligned with the pattern of metal tracksformed by the p-contacts 1364 through the dielectric layer 1362. Hybridbonding may then be performed by first performing dielectric bonding ofthe dielectric layer 1372 with the dielectric layer 1362, and thenperforming metal bonding of p-contacts 1360 with p-contacts 1364. Asdiscussed above with respect to FIG. 9C, the dielectric bonding may beperformed at an ambient temperature (i.e., room temperature). Thedielectric bonding may include performing plasma activation of thedielectric layer 1372 and the dielectric layer 1362. The dielectriclayer 1372 and the dielectric layer 1362 may have high dangling bondstrengths at temperatures greater than or equal to the ambienttemperature. For example, the dielectric layer 1372 and/or thedielectric layer 1362 may include SiCN having a C-content between 25%and 35% and a bond energy between 2,000 mJ/m² and 3,000 mJ/m². Asdiscussed above with respect to FIG. 9D, the metal bonding may beperformed by annealing the LED array 1305 at a higher temperature, suchas between 150° C. and 250° C., in order to form a metal-to-metal bondbetween the p-contacts 1360 and the p-contacts 1364. The metal bondingmay include performing local area thermo-compression bonding of thep-contacts 1360 and the p-contacts 1364.

Alternatively or in addition, reflector layers 1370 may be aligned withn-contacts 1366. For example, the pattern of metal tracks formed by thereflector layers 1370 through the dielectric layer 1372 may be alignedwith the pattern of metal tracks formed by the n-contacts 1366 throughthe dielectric layer 1362. Hybrid bonding may then be performed by firstperforming dielectric bonding of the dielectric layer 1372 with thedielectric layer 1362, and then performing metal bonding of reflectorlayers 1370 with n-contacts 1366. As discussed above with respect toFIG. 9C, the dielectric bonding may be performed at an ambienttemperature (i.e., room temperature). The dielectric bonding may includeperforming plasma activation of the dielectric layer 1372 and thedielectric layer 1362. The dielectric layer 1372 and the dielectriclayer 1362 may have high dangling bond strengths at temperatures greaterthan or equal to the ambient temperature. For example, the dielectriclayer 1372 and/or the dielectric layer 1362 may include SiCN having aC-content between 25% and 35% and a bond energy between 2,000 mJ/m² and3,000 mJ/m². As discussed above with respect to FIG. 9D, the metalbonding may be performed by annealing the LED array 1305 at a highertemperature, such as between 150° C. and 250° C., in order to form ametal-to-metal bond between the reflector layers 1370 and the n-contacts1366. The metal bonding may include performing local areathermo-compression bonding of the reflector layers 1370 and then-contacts 1366.

As shown in FIGS. 13A and 13B, various optics may be formed tocorrespond to the LEDs on an n-side of the LEDs. The optics may beformed after a growth substrate or a temporary substrate is removed fromthe top surface of the LEDs. The optics may be formed before or afterthe hybrid bonding method has been performed. For example, as shown inFIG. 13A, a spherical micro-lens 1342 and a micro-lens 1344 may beformed above their respective LEDs. The spherical micro-lens 1342 andthe micro-lens 1344 may be formed from a direction adjacent to a surfaceof the n-side semiconductor layer 1312 that is opposite to the activelight emitting layer 1314. Similarly, as shown in FIG. 13B, an ARcoating 1382 and a grating 1384 may be formed above their respectiveLEDs. The AR coating 1382 and the grating 1384 may be formed from adirection adjacent to a surface of the n-side semiconductor layer 1352that is opposite to the active light emitting layer 1354. Alternativelyor in addition, n-side processing 1338 may be performed with respect tothe LEDs shown in FIG. 13A. The n-side processing 1338 may be similar tothe n-side processing 1238 described above with reference to FIG. 12A.Alternatively or in addition, p-side processing 1378 may be performedwith respect to the LEDs shown in FIG. 13B. The p-side processing 1378may be similar to the p-side processing 1278 described above withreference to FIG. 12B.

FIG. 14 shows a plot 1400 of the thermal expansion coefficient as afunction of the thermal conductivity for various materials. As shown inFIG. 14 , the thermal expansion coefficient of the III-V semiconductormaterial of the semiconductor layer stack may be different from thethermal expansion coefficient of the Si layer. For example, for blue andgreen LEDs, GaN has a TEC of 3.17 ppm/K at a first crystal orientationand a TEC of 5.59 ppm/K at a second crystal orientation. For infraredLEDs, GaAs/AlGaInAs has a TEC of 5.73 ppm/K. For red LEDs,AlGaAs/AlGaInP has a TEC of 5 ppm/K. In contrast, Si has a TEC of 2.66ppm/K. This may cause wafer bow, cracking, and run-out during thethermal annealing step of the hybrid bonding method. Run-out occurs whenthe centers of the contacts become misaligned. For example, referringback to FIG. 11A, the centers of some or all of the p-contacts 1124 maybecome misaligned with the centers of the respective p-contacts 1120. Insome examples, the contacts near the middle of the wafer may becorrectly aligned, while the contacts near the outer perimeter of thewafer may become misaligned. Accordingly, embodiments of the inventionprovide various methods for compensating this run-out. In some examples,the run-out may be compensated to be less than 200 μm. For example, themaximum misalignment between the centers of the contacts may becompensated to be less than 200 mm for wafers having a maximum lateraldimension of up to 200 mm.

FIG. 15 illustrates an example of an LED array 1500 in which run-out maybe compensated by forming trenches between adjacent LEDs according tocertain embodiments. As shown in FIG. 15 , the LED array 1500 includes aplurality of LEDs 1515 that have a common re-contact. The plurality ofLEDs 1515 are bonded to a substrate 1520 that may be a passive backplaneor an active CMOS Si backplane. The LED array 1500 may also include asubstrate 1510 that may be an LED growth substrate or a temporary bondedsubstrate. As shown in FIG. 15 , a plurality of trenches 1525 may beformed between adjacent LEDs 1515. The trenches 1525 may be formedbefore performing hybrid bonding of the plurality of LEDs 1515 to thesubstrate 1520. In this example, the trenches 1525 extend from thebottom surface of the substrate 1510 to the top surface of the substrate1520. The trenches 1525 may be formed between each pair of adjacent LEDs1515 or between groups of adjacent LEDs 1515. The trenches 1525 may alsobe used to singulate the LEDs 1515 during cool-down. FIGS. 12A and 12Bshow additional examples of trenches 1240 and 1280, respectively.Similarly, FIGS. 13A and 13B show additional examples of trenches 1340and 1380, respectively.

FIG. 16 illustrates another example of an LED array 1600 in whichrun-out may be compensated by forming trenches between adjacent LEDs andby forming corresponding trenches through the substrate according tocertain embodiments. As shown in FIG. 16 , the LED array 1600 includes aplurality of LEDs 1615 that have a common n-contact. The plurality ofLEDs 1615 are bonded to a substrate 1620 that may be a passive backplaneor an active CMOS Si backplane. The LED array 1600 may also include asubstrate 1610 that may be an LED growth substrate. As shown in FIG. 16, a plurality of trenches 1625 may be formed between adjacent LEDs 1615.The trenches 1625 may be formed before performing hybrid bonding of theplurality of LEDs 1615 to the substrate 1620. In this example, thetrenches 1625 extend from the bottom surface of the substrate 1610 tothe top surface of the substrate 1620. The trenches 1625 may be formedbetween each pair of adjacent LEDs 1615 or between groups of adjacentLEDs 1615. Partial trenches 1630 may also be formed through thesubstrate 1610. The partial trenches 1630 may be at least partiallyaligned with the trenches 1625. In some examples, the partial trenches1630 may be formed by sawing through a portion of the substrate 1610.

FIG. 17 illustrates another example of an LED array 1700 in whichrun-out may be compensated by forming trenches between adjacent LEDs andby forming corresponding full through the substrate according to certainembodiments. As shown in FIG. 17 , the LED array 1700 includes aplurality of LEDs 1715 that have a common n-contact. The plurality ofLEDs 1715 are bonded to a substrate 1720 that may be a passive backplaneor an active CMOS Si backplane. The LED array 1700 may also include asubstrate 1710 that may be an LED growth substrate. As shown in FIG. 17, a plurality of trenches 1725 may be formed between adjacent LEDs 1715.The trenches 1725 may be formed before performing hybrid bonding of theplurality of LEDs 1715 to the substrate 1720. In this example, thetrenches 1725 extend from the bottom surface of the substrate 1710 tothe top surface of the substrate 1720. The trenches 1725 may be formedbetween each pair of adjacent LEDs 1715 or between groups of adjacentLEDs 1715. Full trenches 1730 may also be formed through the substrate1710. The full trenches 1730 may be at least partially aligned with thetrenches 1725. In some examples, the full trenches 1730 may be formed bydicing the substrate 1710. Any remaining mismatch of the TECs may bescaled down to a die level of 1 mm×2 mm or 3 mm×5 mm for largetwo-dimensional LED arrays with a high pixel count (such as HD and 2Kdisplays) and a low pixel pitch (such as 1.2 μm to 10 μm).

FIG. 18 illustrates an example of a method 1800 in which run-out may becompensated by changing the shape of components within an LED arrayaccording to certain embodiments. For example, the graph shown on theleft-hand side of FIG. 18 illustrates a curvature profile for GaN-basedLEDs on a Si substrate. As shown in FIG. 18 , the epitaxially-grownGaN-on-Si, which includes a GaN layer 1842 and an Si layer 1840, may beformed to have a concave shape 1812 or a convex shape 1810 afterperforming the dielectric bonding but before performing the metalbonding of the hybrid bonding method. For example, the GaN-on-Si may beformed to have the concave shape 1812 before beginning the ramp-uptemperature 1814. The curvature of an n-GaN buffer 1816 and a p-GaN MQW1818 may change as the GaN-on-Si is heated. The GaN-on-Si has a largecurvature at a temperature between 700° C. and 800° C., a moderatecurvature at a temperature between 150° C. and 250° C., and no curvatureat a temperature of 20° C.

Alternatively or in addition, the run-out may be compensated by forminga TEC compensation layer on the GaN layer 1842 and/or the Si layer 1840.In the example shown on the right-hand side of FIG. 18 , a TECcompensation layer 1870 is formed on the bottom surface of the Si layer1840. The TEC compensation layer 1870 may be formed before performingthe dielectric bonding or before performing the metal bonding of thehybrid bonding method. For example, the TEC compensation layer 1870 maybe a Cu layer having a TEC of 17 ppm/K or a Ni layer having a TEC of 13ppm/K. The higher TEC of the TEC compensation layer 1870 may compensatethe lower TEC of the Si layer (2.66 ppm/K) and match the TEC with atypical III-V semiconductor TEC between 4 ppm/K and 6 ppm/K. The chart1400 shown in FIG. 14 may be referenced to select various materials forthe TEC compensation layer 1870. Further, a Taiko grinding process maybe used to reduce the thickness of the TEC compensation layer 1870 andcustomize the amount of compensation for each III-V material. In otherexamples, a temporary TEC compensation layer (not shown) may be formedon the top surface of the GaN layer 1862. After performing the hybridbonding method, the temporary TEC compensation layer may be removed fromthe top surface of the GaN layer 1862 by using the Taiko grindingprocess, selective etching, and/or laser lift-off (LLO). In otherexamples, a patterned TEC compensation layer may be formed that has gapsbetween adjacent LEDs or groups of LEDs.

Alternatively or in addition, the run-out may be compensated byadjusting the temperature profiles that are applied during the hybridbonding method. The temperatures that are applied to the GaN layer 1842and the Si layer 1840 may be controlled independently, and variousvertical and lateral temperature profiles may be used. A finite elementmethod (FEM) may also simulate and compensate the run-out based onvertical and lateral temperature gradients. Further, the run-out may beminimized by using a laser to perform local area heating and annealing.

Alternatively or in addition, the run-out may be compensated byperforming dishing of various metal components within the LED array. Forexample, p-contacts 1120 shown in FIG. 11A may be dished, as illustratedby gap 1136. Similarly, p-contacts 1220 shown in FIG. 12A may be dished,as illustrated by gap 1236. Likewise, p-contacts 1320 shown in FIG. 13Amay be dished, as illustrated by gap 1336. Using FIG. 11A as an example,other contacts may also be dished, such as p-contacts 1124. Further, theintegrated circuit within the substrate 1128 may be dished. The dishingmay provide better electrical conductivity after the hybrid bondingmethod is performed.

Some or all of the methods discussed above may result in LED arrayshaving improved performance. For example, the hybrid bonding methodallows for high-precision bonding along with both n-side and p-sideprocessing. The hybrid bonding method also allows for reducing surfacerecombination losses by various methods discussed above. Lateral carrierdiffusion may be reduced in the p-side semiconductor layer, the activelight emitting layer, and/or the n-side semiconductor layer. Fewersurface states and defects may result in a lower surface recombinationvelocity (SRV). As discussed in further detail below, lateral (in-plane)carrier confinement may be achieved based on a local e-h-potentialbarrier with quantum-dot (QD) behavior in AlInGaP for red micro-LEDs orInGaN-QD-like behavior for green and blue micro-LEDs based onIn-fluctuations inside the quantum wells.

Various methods may be used to reduce the SRV and the e-h diffusion inmicro-LEDs in conjunction with the hybrid bonding method. For example,sub-surface damage may be addressed by performing a wet chemical etchand adding a dielectric material having a thinner first layer withhigher quality and fewer defects at the heterointerface and a thickersecond layer. Sub-surface damage may also be addressed by performing adry chemical etch, such as inductively coupled plasma (ICP) etching. Thesub-surface damage may be minimized by reducing the physical componentof the etching, such as by reducing the ion energy, and/or by increasingthe chemical component of the etching, such as by using Cl-based etchingwith a high plasma density.

Alternatively or in addition, sidewall passivation may be performed viaa wet chemical surface clean or etch, such as with TMAH, dilute HCl, orsulfidation, and/or by depositing a dielectric material, such as SiN,SiO₂, MN, HfO₂, or GaO. Sidewall passivation may also be performed viaan in-situ surface clean, such as with plasma or hydrogen in anultra-high vacuum (UHV) chamber, and/or by depositing two layers of adielectric material. The first layer of the dielectric material may bedeposited by inductively-coupled plasma enhanced chemical vapordeposition (ICPECVD), atomic layer deposition (ALD), or sputtering. Thefirst layer of the dielectric material may have a thickness between 5 nmand 15 nm. The second layer of the dielectric material may be depositedat a higher rate than the first layer of the dielectric. The secondlayer of the dielectric material may have a thickness between 30 nm and450 nm, such as a thickness between 50 nm and 120 nm. Sidewallpassivation may also be performed via nitridation with an NH₃ or N₂plasma, and/or by depositing a dielectric material.

Alternatively or in addition, overgrowth may be performed via an in-situclean and epitaxial passivation. For example, an UHV clean may beperformed with hydrogen, and molecular beam epitaxy (MBE) overgrowth maybe performed with materials such as ZnSe or AlGaN for red and IRmicro-LEDs, and materials such as AlN, Al₂O₃, or GaO for AlGaN-based UV,blue, green, and red LEDs.

Alternatively or in addition, ion implantation and/or quantum wellintermixing may be performed. Ion implantation is discussed with respectto FIGS. 32-35B and quantum well intermixing is discussed with respectto FIGS. 36A-36C.

As discussed in further detail below, reducing the SRV to 900 cm/s mayincrease the effective internal quantum efficiency (IQE_(eff)). TheIQE_(eff) is the IQE at device level. For red micro-LEDs the peakIQE_(eff) may be 10%, greater than 20%, greater than 40%, or greaterthan 80%, and the surface loss may be reduced to less than 10%. For bluemicro-LEDs the peak IQE_(eff) may be greater than 60%, and the surfaceloss may be reduced to less than 7%. For green micro-LEDs the peakIQE_(eff) may be greater than 45%, and the surface loss may be reducedto less than 10%.

In some examples, for red micro-LEDs the peak IQE_(eff) may be 10% at acurrent density of 1-30 A/cm², and the total wall-plug efficiency (WPE)may be greater than 8% at a current density of 1-30 A/cm². For bluemicro-LEDs the peak IQE_(eff) may be greater than 60% at a currentdensity of 0.1-20 A/cm², the surface loss may be 7%, the SRV may bereduced to 900 cm/s, and the total WPE may be greater than 10% at acurrent density of 0.1-20 A/cm². For green micro-LEDs the peak IQE_(eff)may be greater than 40% at a current density of 0.7-10 A/cm², thesurface loss may be 10%, the SRV may be reduced to 900 cm/s, and thetotal WPE may be greater than 5% at a current density of 0.7-10 A/cm².

Alternatively or in addition, the peak external quantum efficiency (EQE)current may be reduced by using fewer quantum wells, thinner quantumwells, and/or quantum dots. The peak EQE current may be reduced and thecarrier lifetime may be improved to greater than 700 ns by providing lownon-radiative recombination inside the quantum wells and low surfacerecombination loss at the mesa facets. For example, red micro-LEDs mayhave a non-radiative recombination time greater than 1 μsec, while blueand green micro-LEDs may have a non-radiative recombination time greaterthan 0.5 μsec. Red micro-LEDs may have an SRV less than 3E4 cm/s and ane-h diffusion less than 1 cm²/s, and blue and green micro-LEDs may havean SRV less than 1E4 cm/s and an e-h diffusion less than or equal to 2cm²/s.

FIGS. 19A-23 illustrate examples of the improved performance of redmicro-LEDs having a maximum lateral dimension between 1 μm and 10 μm byfull device simulation. These examples reduce the SRV to between 1E4cm/s and 2E4 cm/s, and reduce the lateral e-h diffusion within theactive light emitting region with two-dimensional electron gas (2DEG)and two-dimensional hole gas (2DHG) from 20 cm²/s to 0.07 cm²/s. In someexamples, these results may be achieved via lateral carrier blocking bytechniques such as quantum well intermixing, ion implantation,overgrowth, etc.

FIGS. 19A and 19B show simulated plots of performance parameters for redmicro-LEDs having a vertical mesa shape and a maximum lateral dimensionof 10 μm. FIG. 19A shows a simulated plot 1900 of the total externalquantum efficiency (EQE) as a function of the current density. Curve1920 represents the total EQE of a first standard red micro-LED, curve1915 represents the total EQE of a first improved red micro-LED having aSRV of 3E4 cm/s and an e-h diffusion of 20 cm²/s, and curve 1910represents the total EQE of a second improved red micro-LED having anSRV of 2E4 cm/s and an e-h diffusion of 0.07 cm²/s. Arrow 1925 indicatesthe improvement in total EQE between the first standard red micro-LEDand the first improved red micro-LED, arrow 1930 indicates theimprovement in total EQE between the first improved red micro-LED andthe second improved red micro-LED, and arrow 1935 indicates theimprovement in total EQE between the first standard red micro-LED andthe second improved red micro-LED. The second improved red micro-LED hasa six-fold increase in total EQE as compared with the first standard redmicro-LED. The improvement is particularly large at low currentdensities. FIG. 19B shows a simulated plot 1905 of the SRV as a functionof the energy gap for various materials. The SRV values shown in FIG.19B are used for the simulations discussed herein.

FIGS. 20A and 20B show simulated plots of additional performanceparameters for red micro-LEDs having a vertical mesa shape and a maximumlateral dimension of 10 μm. FIG. 20A shows a simulated plot 2000 of theeffective internal quantum efficiency (IQE_(eff)) as a function of thecurrent density. Curve 2015 represents the IQE_(eff) of the firstimproved red micro-LED having a SRV of 3E4 cm/s and an e-h diffusion of20 cm²/s, and curve 2010 represents the IQE_(eff) of the second improvedred micro-LED having an SRV of 2E4 cm/s and an e-h diffusion of 0.07cm²/s. The IQE_(eff) may be improved to various values, such as 10%,greater than 20%, greater than 40%, or greater than 80%. FIG. 20B showsa simulated plot 2005 of the surface loss as a function of the currentdensity. Curve 2025 represents the surface loss of the first improvedred micro-LED having a SRV of 3E4 cm/s and an e-h diffusion of 20 cm²/s,and curve 2020 represents the surface loss of the second improved redmicro-LED having an SRV of 2E4 cm/s and an e-h diffusion of 0.07 cm²/s.In some examples, the surface loss may be reduced from 99% to 10%.

FIGS. 21A and 21B show simulated plots of performance parameters for redmicro-LEDs having a vertical mesa shape and a maximum lateral dimensionof 10 μm, along with red micro-LEDs having a parabolic mesa shape and amaximum lateral dimension of 3 μm. FIG. 21A shows a simulated plot 2100of the total EQE as a function of the current density. Curve 2120represents the total EQE of the first standard red micro-LED, curve 2115represents the total EQE of the first improved red micro-LED having aSRV of 3E4 cm/s and an e-h diffusion of 20 cm²/s, and curve 2125represents the total EQE of the second improved red micro-LED having anSRV of 2E4 cm/s and an e-h diffusion of 0.07 cm²/s. For comparison,curve 2110 represents the total EQE of a third improved red micro-LEDhaving a parabolic mesa shape, an additional lens, an anti-reflection(AR) coating, and a maximum lateral dimension of 3 μm. The thirdimproved red micro-LED also has an SRV of 2E4 cm/s and an e-h diffusionof 0.07 cm²/s. Curve 2135 represents the total EQE of a second standardred micro-LED having a parabolic mesa shape and a maximum lateraldimension of 3.1 μm. Arrow 2130 indicates the improvement in total EQEbetween the second standard red micro-LED and the third improved redmicro-LED.

FIG. 21B shows a simulated plot 2105 of the total EQE as a function ofthe current. Curve 2150 represents the total EQE of the first standardred micro-LED, curve 2145 represents the total EQE of the first improvedred micro-LED having a SRV of 3E4 cm/s and an e-h diffusion of 20 cm²/s,and curve 2155 represents the total EQE of the second improved redmicro-LED having an SRV of 2E4 cm/s and an e-h diffusion of 0.07 cm²/s.For comparison, curve 2140 represents the total EQE of a third improvedred micro-LED having a parabolic mesa shape, an additional lens, ananti-reflection (AR) coating, and a maximum lateral dimension of 3 μm.The third improved red micro-LED also has an SRV of 2E4 cm/s and an e-hdiffusion of 0.07 cm²/s. Curve 2170 represents the total EQE of thesecond standard red micro-LED having a parabolic mesa shape and amaximum lateral dimension of 3.1 μm. Arrow 2160 indicates theimprovement in total EQE between the second standard red micro-LED andthe third improved red micro-LED, and arrow 2165 indicates theimprovement in total EQE between the first standard red micro-LED andthe third improved red micro-LED. The third improved red micro-LEDhaving the parabolic mesa shape, the additional lens, the AR coating,and the maximum lateral dimension of 3 μm may have a thirty-fold highertotal EQE than the standard red micro-LEDs.

FIGS. 22A and 22B show simulated plots of additional performanceparameters for red micro-LEDs having a vertical mesa shape and a maximumlateral dimension of 10 μm, along with red micro-LEDs having a parabolicmesa shape and a maximum lateral dimension of 3 μm. FIG. 22A shows asimulated plot 2200 of the total wall-plug efficiency (WPE) as afunction of the current density. Curve 2215 represents the total WPE ofthe first improved red micro-LED having a SRV of 3E4 cm/s and an e-hdiffusion of 20 cm²/s, curve 2225 represents the total WPE of the secondimproved red micro-LED having an SRV of 2E4 cm/s and an e-h diffusion of0.07 cm²/s, and curve 2210 represents the total WPE of the thirdimproved red micro-LED having a parabolic mesa shape, an additionallens, an AR coating, and a maximum lateral dimension of 3 μM.

FIG. 22B shows a simulated plot 2205 of the total WPE as a function ofthe current. Curve 2235 represents the total WPE of the first improvedred micro-LED having a SRV of 3E4 cm/s and an e-h diffusion of 20 cm²/s,curve 2245 represents the total WPE of the second improved red micro-LEDhaving an SRV of 2E4 cm/s and an e-h diffusion of 0.07 cm²/s, and curve2230 represents the total WPE of the third improved red micro-LED havinga parabolic mesa shape, an additional lens, an anti-reflection (AR)coating, and a maximum lateral dimension of 3 μm. The third improved redmicro-LED also has an SRV of 2E4 cm/s and an e-h diffusion of 0.07cm²/s. The third improved red micro-LED having the parabolic mesa shape,the additional lens, the AR coating, and the maximum lateral dimensionof 3 μm may have a total WPE of approximately 30% at a current of 10 μA.

FIG. 23 shows a simulated plot 2300 of brightness for red micro-LEDshaving a parabolic mesa shape, an additional lens, an AR coating, and amaximum lateral dimension between 1 μm and 3 μm. The brightness ismeasured within an angle of ±10° with respect to an emission axis of theLEDs. Curve 2330 represents the brightness of a standard red micro-LED,curve 2325 represents the brightness of a first optimized micro-LEDhaving a maximum lateral dimension of 3 μm, an SRV of 1E5 cm/s, and ane-h diffusion of 20 cm²/s, curve 2320 represents the brightness of asecond optimized micro-LED having a maximum lateral dimension of 3 μm,an SRV of 3E4 cm/s, and an e-h diffusion of 20 cm²/s, curve 2315represents the brightness of a third optimized micro-LED having amaximum lateral dimension of 3 μm, an SRV of 3E4 cm/s, and an e-hdiffusion of 1 cm²/s, and curve 2310 represents the brightness of afourth optimized micro-LED having a maximum lateral dimension of 3 μm,an SRV of 1E4 cm/s, and an e-h diffusion of 0.1 cm²/s. For example, abrightness between 10 and 20 Mnits may be achieved at a current of 1 μA,and a brightness of 150 Mnits may be achieved at a current of 10 μA.

FIGS. 24A-27 illustrate examples of the improved performance of greenmicro-LEDs having a reduced SRV of 900 cm/s and a reduced lateral e-hdiffusion of 2 cm²/s. As discussed in further detail below, these greenmicro-LEDs take a higher density of states between 40 meV and 60 meVinto account, based on In-fluctuations in the InGaN quantum well, toachieve a higher efficiency.

FIGS. 24A and 24B show simulated plots of performance parameters forgreen micro-LEDs having a vertical mesa shape and five quantum wells.FIG. 24A shows a simulated plot 2400 of the surface loss as a functionof the current. Curve 2410 represents the surface loss of a firstimproved green micro-LED having dimensions of 1 μm×1 μm and an SRV of900 cm/s, and curve 2415 represents the surface loss of a secondimproved green micro-LED having dimensions of 10 μm×10 μm and an SRV of900 cm/s. Curve 2420 represents the surface loss of a first improvedarray of green micro-LEDs having dimensions of 1000 μm×1000 μm. FIG. 24Bshows a simulated plot 2430 of the IQE_(eff) as a function of thecurrent. Curve 2430 represents the IQE_(eff) of a third improved greenmicro-LED having dimensions of 8.5 μm×8.5 μm and an SRV of 900 cm/s.Curve 2435 represents the IQE_(eff) of the first improved array of greenmicro-LEDs having dimensions of 1000 μm×1000 μm. As shown in FIGS. 24Aand 24B, the surface loss may be reduced to approximately 10% at acurrent of 1 μA, and the IQE_(eff) may be increased to a value between50% and 60%.

FIG. 25 shows a simulated plot 2500 of the total EQE for greenmicro-LEDs as a function of the current. The total EQE is measuredwithin an angle of ±90° with respect to an emission axis of the LEDs.Curve 2520 represents the total EQE of a first standard green micro-LEDhaving a vertical mesa shape and a maximum lateral dimension of 10 μm,and curve 2525 represents the total EQE of a second standard greenmicro-LED having a semi-parabolic mesa shape and a maximum lateraldimension of 3.9 μm. Curve 2530 represents the total EQE of the firstimproved green micro-LED having dimensions of 1 μm×1 μm and a verticalmesa shape, curve 2515 represents the total EQE of the third improvedgreen micro-LED having dimensions of 8.5 μm×8.5 μm and a vertical mesashape, and curve 2510 represents the total EQE of a fourth improvedgreen micro-LED having a maximum lateral dimension of 3 μm, a parabolicmesa shape, an additional lens, and an AR coating. Curve 2535 representsthe total EQE of the first improved array of green micro-LEDs havingdimensions of 1000 μm×1000 μm. As shown in FIG. 25 , the fourth improvedgreen micro-LED may have a total EQE of approximately 20% at a currentbetween 0.1 and 1.0 μA.

FIG. 26 shows a simulated plot 2600 of the total WPE for greenmicro-LEDs as a function of the current. The total WPE is measuredwithin an angle of ±90° with respect to an emission axis of the LEDs.Curve 2630 represents the total WPE of the first improved greenmicro-LED having dimensions of 1 μm×1 μm and a vertical mesa shape,curve 2615 represents the total EQE of the third improved greenmicro-LED having dimensions of 8.5 μm×8.5 μm and a vertical mesa shape,curve 2610 represents the total WPE of the fourth improved greenmicro-LED having a maximum lateral dimension of 3 μm, a parabolic mesashape, an additional lens, and an AR coating, and curve 2620 representsthe total WPE of a fifth improved green micro-LED having dimensions of 3μm×3 μm and a vertical mesa shape. Curve 2635 represents the total WPEof the first improved array of green micro-LEDs having dimensions of1000 μm×1000 μm. As shown in FIG. 26 , the fourth improved greenmicro-LED may have a total WPE of approximately 18% at a current between100 nA and 300 nA.

FIG. 27 shows a simulated plot 2700 of the brightness for greenmicro-LEDs as a function of the current. The brightness is measuredwithin an angle of ±10° with respect to an emission axis of the LEDs.Curve 2725 represents the brightness of the second standard greenmicro-LED having a semi-parabolic mesa shape and a maximum lateraldimension of 3.9 μm. Curve 2715 represents the brightness of the firstimproved green micro-LED having dimensions of 1 μm×1 μm and a verticalmesa shape, curve 2730 represents the brightness of the third improvedgreen micro-LED having dimensions of 8.5 μm×8.5 μm and a vertical mesashape, and curve 2710 represents the brightness of the fourth improvedgreen micro-LED having a maximum lateral dimension of 3 μm, a parabolicmesa shape, an additional lens, and an AR coating. Curve 2735 representsthe brightness of the first improved array of green micro-LEDs havingdimensions of 1000 μm×1000 μm. As shown in FIG. 27 , the fourth improvedgreen micro-LED may have a brightness of approximately 30 Mnits at acurrent of 1 μA and a brightness of approximately 150 Mnits at a currentof 10 μA.

FIGS. 28A-30 illustrate examples of the improved performance of bluemicro-LEDs having a reduced SRV of 900 cm/s and a reduced lateral e-hdiffusion of 2 cm²/s. These micro-LEDs have a density of states between20 meV and 35 meV.

FIGS. 28A and 28B show simulated plots of performance parameters forblue micro-LEDs having a vertical mesa shape. FIG. 28A shows a simulatedplot 2800 of the surface loss as a function of the current. Curve 2810represents the surface loss of a first improved blue micro-LED having asingle quantum well, a vertical mesa shape, dimensions of 1 μm×1 μm, andan SRV of 900 cm/s, curve 2815 represents the surface loss of a secondimproved blue micro-LED having a single quantum well, a vertical mesashape, dimensions of 8.5 μm×8.5 μm, and an SRV of 900 cm/s, and curve2820 represents the surface loss of a third improved blue micro-LEDhaving a single quantum well, a vertical mesa shape, dimensions of 90μm×90 μm, and an SRV of 900 cm/s. Curve 2825 represents the surface lossof a first improved array of blue micro-LEDs having a single quantumwell, a vertical mesa shape, and dimensions of 1000 μm×1000 μm. FIG. 28Bshows a simulated plot 2805 of the IQE_(eff) as a function of thecurrent. Curve 2830 represents the IQE_(eff) of a fourth improved bluemicro-LED having a single quantum well, a vertical mesa shape,dimensions of 8.5 μm×8.5 μm, and an SRV of 900 cm/s. Curve 2840represents the IQE_(eff) of the first improved array of blue micro-LEDshaving a single quantum well, a vertical mesa shape, and dimensions of1000 μm×1000 μm. Curve 2835 represents the IQE_(eff) of a secondimproved array of blue micro-LEDs having seven quantum wells, a verticalmesa shape, and dimensions of 1000 μm×1000 μm. As shown in FIGS. 28A and28B, the surface loss may be reduced to approximately 7% at a current of1 μA, and the IQE_(eff) may be increased to approximately 70% at acurrent of 1 μA.

FIGS. 29A and 29B show simulated plots of additional performanceparameters for blue micro-LEDs having a vertical mesa shape. FIG. 29Ashows a simulated plot 2900 of the total EQE as a function of thecurrent. The total EQE is measured within an angle of ±90° with respectto an emission axis of the LEDs. Curve 2920 represents the total EQE ofa standard blue micro-LED having a parabolic mesa shape and a maximumlateral dimension of 3.9 μm. Curve 2910 represents the total EQE of afifth improved blue micro-LED having a single quantum well, a parabolicmesa shape, a maximum lateral dimension of 3.0 μm, and no SRV of 900cm/s, and curve 2915 represents the total EQE of a sixth improved bluemicro-LED having a single quantum well, a parabolic mesa shape, amaximum lateral dimension of 3.0 μm, and an SRV of 900 cm/s. FIG. 29Bshows a simulated plot 2905 of the total WPE as a function of thecurrent. The total WPE is measured within an angle of ±90° with respectto an emission axis of the LEDs. Curve 2920 represents the total WPE ofthe fourth improved blue micro-LED having a single quantum well, avertical mesa shape, dimensions of 8.5 μm×8.5 μm, and an SRV of 900cm/s, curve 2935 represents the total WPE of a seventh improved bluemicro-LED having seven quantum wells and dimensions of 8.5 μm×8.5 μm,and curve 2940 represents the total WPE of an eighth improved bluemicro-LED having a single quantum well, a vertical mesa shape,dimensions of 90 μm×90 μm, and an SRV of 3E4 cm/s. Curve 2950 representsthe total WPE of the second improved array of blue micro-LEDs havingseven quantum wells, a vertical mesa shape, and dimensions of 1000μm×1000 μm, and curve 2945 represents the total WPE of a third improvedarray of blue micro-LEDs having a single quantum well, a vertical mesashape, and dimensions of 1000 μm×1000 μm, and an SRV of 3E4 cm/s. Asshown in FIGS. 29A and 29B, the total EQE of the sixth improved bluemicro-LED may be approximately 30% at a current of 100 nA, and the totalWPE of the fourth improved blue micro-LED may be approximately 12% at acurrent of 100 nA.

FIG. 30 shows a simulated plot 3000 of the brightness for bluemicro-LEDs as a function of the current. The brightness is measuredwithin an angle of ±10° with respect to an emission axis of the LEDs.Curve 3010 represents the brightness of the fifth improved bluemicro-LED having a single quantum well, a parabolic mesa shape, anadditional lens, an AR coating, a maximum lateral dimension of 3.0 μm,and no SRV, curve 3015 represents the brightness of the sixth improvedblue micro-LED having a single quantum well, a parabolic mesa shape, anadditional lens, an AR coating, a maximum lateral dimension of 3.0 μm,and an SRV of 900 cm/s, curve 3020 represents the brightness of a ninthimproved blue micro-LED having a single quantum well, a vertical mesashape, dimensions of 3 μm×3 μm, and an SRV of 900 cm/s, curve 3025represents the brightness of the first improved blue micro-LED having asingle quantum well, a vertical mesa shape, dimensions of 1 μm×1 μm, andan SRV of 900 cm/s, curve 3030 represents the brightness of the fourthimproved blue micro-LED having a single quantum well, a vertical mesashape, dimensions of 8.5 μm×8.5 μm, and an SRV of 900 cm/s, and curve3035 represents the brightness of the third improved blue micro-LEDhaving a single quantum well, a vertical mesa shape, dimensions of 90μm×90 μm, and an SRV of 900 cm/s. Curve 3045 represents the brightnessof the first improved array of blue micro-LEDs having a single quantumwell, a vertical mesa shape, and dimensions of 1000 μm×1000 μm, andcurve 3040 represents the brightness of the second improved array ofblue micro-LEDs having seven quantum wells, a vertical mesa shape, anddimensions of 1000 μm×1000 μm. As shown in FIG. 30 , the fifth improvedblue micro-LED and the sixth improved blue micro-LED may have abrightness of approximately 4 Mnits at a current of 1 μA and abrightness of approximately 30 Mnits at a current of 10 μA.

FIGS. 31A-31C illustrate an example of the use of alloy and strainfluctuations to confine lateral carriers according to certainembodiments. Alloy and strain fluctuations, such as In/Ga in the activeregion of InGaN quantum wells, may create a local e-h potential barrierthat blocks lateral carrier diffusion to the mesa facet, especially atlower current densities. For example, blue and green InGaN-basedmicro-LEDs can reduce lateral carrier diffusion due to InGaN-alloyfluctuations, and red AlInGaP-based micro-LEDs can reduce lateralcarrier diffusion due to AlInGaP-alloy fluctuations. Blue micro-LEDs mayhave a density of states that is greater than 20 meV, green micro-LEDsmay have a density of states that is greater than 40 meV, and greenmicro-LEDs may have a density of states that is greater than 60 meV.

FIGS. 31A and 31C show an example of a model of localized states basedon potential fluctuations due to inhomogeneities in In-rich InGaNquantum wells. FIG. 31A shows a bandgap diagram 3100 including electrons3120 and holes 3125 that may produce spontaneous emission 3130,stimulated emission 3135, and/or non-radiative recombination 3140. FIG.31B shows a plot 3105 of the energy as a function of the joint densityof states. Mobile states 3150 have an energy above the mobility edgeE_(me), while localized states 3155 have an energy below the mobilityedge E_(me). Carriers below the mobility edge E_(me) are trapped withinthe localized states 3155. FIG. 31C shows an experimental plot 3110 ofthe carrier lifetime 3165 as a function of the energy, along with thenormalized intensity at maximum 3160 as a function of the energy. Acurve fit of the carrier lifetime 3165 may be performed to determine thelocalization depth of the carriers. In the example shown in FIG. 31C,the curve fit results in a radiative lifetime of 999 ps, a mobility edgeE_(me) of 2.84 eV, and an average depth E₀ of 57 meV.

FIG. 32 illustrates an example of ion implantation that may be performedaccording to certain embodiments. The method illustrated in FIG. 32 mayreduce lateral carrier mobility and surface recombination by using ionimplantation to disrupt the semiconductor lattice outside of a centralportion of the micro-LED. The ion implantation reduces the number ofelectrons that reach the outer surface of the micro-LED, and thereforereduces the amount of surface recombination. Bombarding thesemiconductor material with high-energy ions has two effects. First, thelattice of the semiconductor material becomes less electricallyconductive, so the current does not spread through the entire structurein all directions, and instead is funneled vertically through thecentral region. Second, the diffusivity is reduced in the bombardedregion, such that the electrons do not move as far laterally. Both thediffusivity D and the electron diffusion length L are reduced by the ionimplantation.

FIG. 32 shows a micro-LED 3200 that undergoes ion implantation 3280before a mesa structure is formed from the semiconductor layer stack. Asshown in FIG. 32 , the micro-LED 3200 includes an n-side semiconductorlayer 3210, a p-side semiconductor layer 3215, and an active lightemitting layer 3220. Together the n-side semiconductor layer 3210, thep-side semiconductor layer 3215, and the active light emitting layer3220 form a semiconductor layer stack 3290. The semiconductor layerstack 3290 may include any suitable material, such as a group IIInitride, a group III phosphide, or a group III arsenide. The n-sidesemiconductor layer 3210 may be formed on a substrate 3225, and may havea light outcoupling surface 3230. The diameter of the light outcouplingsurface 3230 may be less than 10 μm. A p-contact 3240 may be formed on atop surface of the p-side semiconductor layer 3215, and a resist 3250may be formed on a top surface of the p-contact 3240. The p-contact 3240may be made of a metal, such as titanium or gold.

The p-contact 3240 and the resist 3250 may be used as a mask to definean outer region of the semiconductor layer stack 3290 where the ions areimplanted. The outer region will include the portions of thesemiconductor layer stack 3290 that are not shaded by the mask duringion implantation. If the ions are incident at an angle of 0° withrespect to an axis that is normal to a plane of the mask (i.e. the planeof the mask is along the horizontal direction in FIG. 32 ), the outerregion will include the portions of the semiconductor layer stack 3290that are not directly beneath the mask. On the other hand, if the ionsare incident at an angle that is greater than 0° with respect to theaxis that is normal to a plane of the mask, the outer region willinclude the portions of the semiconductor layer stack 3290 that are notshaded by the mask, thereby forming an outer region having interioredges that are sloped at the angle of implantation. For example, theions may be implanted at an angle between 0° and 7° with respect to theaxis that is normal to the plane of the mask.

As shown in FIG. 32 , ion implantation 3280 may be performed before thesemiconductor layer stack 3290 is formed into a mesa shape. The mesashape may be planar, vertical, conical, semi-parabolic, and/orparabolic. Alternatively, ion implantation may be performed after thesemiconductor layer stack 3290 is formed into the mesa shape. In thisexample, the energy of the ions would be reduced.

Various ions may be used, such as H or He ions. The implantation patternmay be controlled by adjusting the implantation angle, the ion energy,the types of ions, and/or the masking of the implantation region. Forexample, the depth to which the ions are implanted may be varied bychanging the energy of the ions. H and He ions may be implanted with anenergy between 20 keV and 140 keV. For example, for red micro-LEDs, a 20keV implantation energy may result in an implantation depth of 200 nm,an 80 keV implantation energy may result in an implantation depth of 600nm, and a 140 keV implantation energy may result in an implantationdepth of 1000 nm. The implantation energy for thinner p-side micro-LEDs,such as blue and green GaN-based micro-LEDs, may range from 5 keV to 120keV. On the other hand, the implantation energy for thicker p-sidemicro-LEDs, such as infrared (IR) micro-LEDs, may range from 80 keV to400 keV. The implantation dose of the ions may be between 1×10¹⁴ cm⁻²and 1×10¹⁶ cm⁻². The lateral carrier diffusion in the outer region ofthe semiconductor layer stack 3290 may be reduced to less than 1 cm²/sby performing ion implantation.

FIGS. 33A, 33B, and 34 show various ion implantation depths formicro-LEDs according to certain embodiments. FIG. 34 shows additionaldetails of the micro-LED shown in FIG. 33A. FIG. 33A shows an infraredmicro-LED 3300 that emits light at 940 nm, and FIG. 33B shows a redmicro-LED 3305 that emits light at 630 nm. In the examples shown inFIGS. 33A and 33B, the first implantation depth 3390 is 200 nm, thesecond implantation depth 3392 is 600 nm, and the third implantationdepth 3394 is 1000 nm. FIG. 34 shows an infrared micro-LED 3400 that isthe same as the infrared micro-LED 3300 shown in FIG. 33A.

As shown in FIGS. 33A and 34 , the semiconductor layer stack of themicro-LED 3300/3400 includes a p-side semiconductor layer 3415 that hasa 50 nm thick GaAs layer, a 50 nm thick Al_(0.09)Ga_(0.91)As layer, anda 500 nm thick Al_(0.3)Ga_(0.7)As layer. The semiconductor layer stackof the micro-LED 3400 also includes a 300 nm thick InGaAs/GaAsP multiplequantum well (MQW) layer 3420 that is an active light emitting layer,and an n-side semiconductor layer 3410 that has a 500 nm thickAl_(0.17)Ga_(0.83)As layer. The semiconductor layer stack is formed on aGaAs substrate 3425. The first implantation depth 3490 extends from thetop of the p-side semiconductor layer 3415 through a depth within the500 nm thick Al_(0.3)Ga_(0.7)As layer. The second implantation depth3492 extends from the top of the p-side semiconductor layer 3415 throughthe interface between the p-side semiconductor layer 3415 and the activelight emitting layer 3420. The third implantation depth 3494 extendsfrom the top of the p-side semiconductor layer 3415 through a depthwithin the n-side semiconductor layer 3410. The micro-LED 3400 includesa p-contact 3440 and a resist 3450 that are used as a mask during ionimplantation 3480.

As shown in FIG. 33B, the semiconductor layer stack of the micro-LED3305 includes a p-side semiconductor layer that has a 200 nm thick GaPlayer, a 90 nm thick In_(0.49)Al_(0.51)P layer, and a 10 nm thickIn_(0.5)Al_(0.25)Ga_(0.25)P layer. The semiconductor layer stack of themicro-LED 3305 also includes a 180 nm thick InGaP/InAlGaP MQW layer thatis an active light emitting layer, and an n-side semiconductor layerthat has a 4500 nm thick Al_(0.6)Ga_(0.4)As layer. The semiconductorlayer stack is formed on a GaAs substrate. The first implantation depth3390 extends from the top of the p-side semiconductor layer to theinterface between the p-side semiconductor layer and the active lightemitting layer. The second implantation depth 3392 and the thirdimplantation depth 3394 extend from the top of the p-side semiconductorlayer through different depths within the n-side semiconductor layer.

As shown in FIGS. 33A and 33B, the ions may be implanted to variousdepths within the micro-LED. For example, the ions may be implanted froma top surface of the p-side semiconductor layer to a depth within thep-side semiconductor layer. Alternatively, the ions may be implantedfrom a top surface of the p-side semiconductor layer to a depth withinthe active light emitting layer. As another option, the ions may beimplanted from a top surface of the p-side semiconductor layer to adepth within the n-side semiconductor layer.

FIGS. 35A and 35B show measurements of characteristics of micro-LEDs forwhich ion implantation has been performed according to certainembodiments. Specifically, measurements were performed on infraredmicro-LEDs that were implanted with H ions to a depth within the activelight emitting layer. FIG. 35A shows a plot 3500 of the current as afunction of the voltage. FIG. 35B shows a plot 3505 of the LOP in anumerical aperture (NA) of 0.5 as a function of the current. Curve 3510represents the LOP of a micro-LED having a parabolic mesa shape that wasimplanted with H ions, and curve 3515 represents the LOP of a micro-LEDhaving a planar mesa shape that was implanted with H ions. In contrast,curve 3520 represents the LOP of a micro-LED having a parabolic mesashape that was not implanted with H ions, and curve 3515 represents theLOP of a micro-LED having a planar mesa shape that was not implantedwith H ions. Arrow 3530 indicates the improvement in LOP for themicro-LED having the parabolic mesa shape, and arrow 3535 indicates theimprovement in LOP for the micro-LED having the planar mesa shape. Asshown in FIG. 35B, each of the micro-LEDs demonstrated a two-foldincrease in LOP at higher currents.

FIGS. 36A-36C illustrate an example of quantum well intermixing that maybe performed according to certain embodiments. The method shown in FIGS.36A-36C may reduce lateral carrier mobility and surface recombination byusing quantum well intermixing to change the composition of areas of thesemiconductor layer stack outside of the central portion of themicro-LED. The quantum well intermixing reduces the number of electronsthat reach the outer surface of the micro-LED, and therefore reduces theamount of surface recombination.

As shown in FIG. 36A, a micro-LED 3600 may include an outer region 3635where quantum well intermixing is performed, along with a central region3620 where quantum well intermixing is not performed. In some examples,quantum well intermixing may be used to increase the bandgap in theouter region 3635 of the semiconductor layer stack by implanting ions inthe outer region 3635 of the semiconductor layer stack and subsequentlyannealing the outer region 3635 of the semiconductor layer stack tointermix the ions with atoms within the outer region 3620 of thesemiconductor layer stack. The ions may be implanted according to themethods discussed above with regard to FIG. 32 . The outer region 3620of the semiconductor layer stack may be defined by a mask, such as thep-contact 3240 and the resist 3250 described above with reference toFIG. 32 . For quantum well intermixing, various ions may be used, suchas Al ions. The Al ions may be implanted with an energy of approximately400 keV, which may result in an implantation depth of approximately 460nm. More generally, the Al ions may be implanted with an energy between80 keV and 400 keV.

For example, if the semiconductor layer stack is made of AlInGaP, extraAl may be added at the edges of the quantum wells in the outer region3635. This increases the bandgap at the edges of the quantum wells, suchthat the band structure is flat in the center, the conduction band bendsupward at the edges, and/or the valence band bends downward at theedges. Accordingly, when electrons are injected from the top of thep-side semiconductor layer, they can freely diffuse in the lateraldirection, but are repelled by the higher band structure at the edges,which prevents them from escaping from the side of the structure. Forexample, the concentration of Al may be increased from 0.3 to 0.5 at theedges of the outer region 3635. The outer region 3635 may form across-sectional annular shape. The electrons may be partly or entirelyconfined to a central area of the light emitting region corresponding tothe central region 3620 of the semiconductor layer stack.

In other examples, the micro-LED 3600 may include a cap layer 3630 thatis unstrained or lightly strained. The cap layer 3630 may have adiameter of approximately 1 μm. In addition, the micro-LED 3600 mayinclude a dielectric layer 3625 that is highly strained. For example,the dielectric layer 3625 may have a higher level of strain than the caplayer 3630. The dielectric layer 3625 may include a dielectric materialsuch as SiN or SiO₂. Quantum well intermixing may be performed byimpurity-free vacancy disordering (IFVD), the strained dielectric layer3625, and annealing. This provides strain-induced quantum wellintermixing of Al within the outer region 3635. Another example of amethod of quantum well intermixing is impurity-induced disordering (IID)with Zn-diffusion and intermixing, in which Zn-diffusion is performedwith an As-overpressure in a chamber, such as an MOVPE reactor or aglass furnace. Yet another example of a method of quantum wellintermixing is creating strained SiN by mixed frequency SiN-PECVD. Thelow frequency (LF) may be 680 kHz while the high frequency (HF) may be13.56 MHz.

As shown in FIG. 36B, a micro-LED 3605 may include an outer region 3655where quantum well intermixing is performed, along with a central region3640 where quantum well intermixing is not performed. In addition, themicro-LED may include a cap layer 3650 that is unstrained or lightlystrained, and a dielectric layer 3645 that is highly strained. Forexample, the dielectric layer 3645 may have a higher level of strainthan the cap layer 3650. These components may be similar to thosediscussed above with regard to FIG. 36A, except that the cap layer 3650may be thinner than the cap layer 3630, and the dielectric layer 3645may extend down the sides of the semiconductor layer stack.

As shown in FIG. 36C, a micro-LED 3610 may include an outer region 3675where quantum well intermixing is performed, along with a central region3660 where quantum well intermixing is not performed. In addition, themicro-LED may include a cap layer 3670 that is unstrained or lightlystrained, and a dielectric layer 3665 that is highly strained. Forexample, the dielectric layer 3665 may have a higher level of strainthan the cap layer 3670. These components may be similar to thosediscussed above with regard to FIG. 36A, except that the cap layer 3670may be narrower than the cap layer 3630, and the dielectric layer 3665may extend down the sides of the semiconductor layer stack. Also, thesemiconductor layer stack may have a parabolic mesa shape instead of avertical mesa shape.

Embodiments disclosed herein may be used to implement components of anartificial reality system or may be implemented in conjunction with anartificial reality system. Artificial reality is a form of reality thathas been adjusted in some manner before presentation to a user, whichmay include, for example, a virtual reality, an augmented reality, amixed reality, a hybrid reality, or some combination and/or derivativesthereof. Artificial reality content may include completely generatedcontent or generated content combined with captured (e.g., real-world)content. The artificial reality content may include video, audio, hapticfeedback, or some combination thereof, and any of which may be presentedin a single channel or in multiple channels (such as stereo video thatproduces a three-dimensional effect to the viewer). Additionally, insome embodiments, artificial reality may also be associated withapplications, products, accessories, services, or some combinationthereof, that are used to, for example, create content in an artificialreality and/or are otherwise used in (e.g., perform activities in) anartificial reality. The artificial reality system that provides theartificial reality content may be implemented on various platforms,including an HMD connected to a host computer system, a standalone HMD,a mobile device or computing system, or any other hardware platformcapable of providing artificial reality content to one or more viewers.

FIG. 37 is a simplified block diagram of an example electronic system3700 of an example near-eye display (e.g., HMD device) for implementingsome of the examples disclosed herein. Electronic system 3700 may beused as the electronic system of an HMD device or other near-eyedisplays described above. In this example, electronic system 3700 mayinclude one or more processor(s) 3710 and a memory 3720. Processor(s)3710 may be configured to execute instructions for performing operationsat a number of components, and can be, for example, a general-purposeprocessor or microprocessor suitable for implementation within aportable electronic device. Processor(s) 3710 may be communicativelycoupled with a plurality of components within electronic system 3700. Torealize this communicative coupling, processor(s) 3710 may communicatewith the other illustrated components across a bus 3740. Bus 3740 may beany subsystem adapted to transfer data within electronic system 3700.Bus 3740 may include a plurality of computer buses and additionalcircuitry to transfer data.

Memory 3720 may be coupled to processor(s) 3710. In some embodiments,memory 3720 may offer both short-term and long-term storage and may bedivided into several units. Memory 3720 may be volatile, such as staticrandom access memory (SRAM) and/or dynamic random access memory (DRAM)and/or non-volatile, such as read-only memory (ROM), flash memory, andthe like. Furthermore, memory 3720 may include removable storagedevices, such as secure digital (SD) cards. Memory 3720 may providestorage of computer-readable instructions, data structures, programmodules, and other data for electronic system 3700. In some embodiments,memory 3720 may be distributed into different hardware modules. A set ofinstructions and/or code might be stored on memory 3720. Theinstructions might take the form of executable code that may beexecutable by electronic system 3700, and/or might take the form ofsource and/or installable code, which, upon compilation and/orinstallation on electronic system 3700 (e.g., using any of a variety ofgenerally available compilers, installation programs,compression/decompression utilities, etc.), may take the form ofexecutable code.

In some embodiments, memory 3720 may store a plurality of applicationmodules 3722 through 3724, which may include any number of applications.Examples of applications may include gaming applications, conferencingapplications, video playback applications, or other suitableapplications. The applications may include a depth sensing function oreye tracking function. Application modules 3722-3724 may includeparticular instructions to be executed by processor(s) 3710. In someembodiments, certain applications or parts of application modules3722-3724 may be executable by other hardware modules 3780. In certainembodiments, memory 3720 may additionally include secure memory, whichmay include additional security controls to prevent copying or otherunauthorized access to secure information.

In some embodiments, memory 3720 may include an operating system 3725loaded therein. Operating system 3725 may be operable to initiate theexecution of the instructions provided by application modules 3722-3724and/or manage other hardware modules 3780 as well as interfaces with awireless communication subsystem 3730 which may include one or morewireless transceivers. Operating system 3725 may be adapted to performother operations across the components of electronic system 3700including threading, resource management, data storage control and othersimilar functionality.

Wireless communication subsystem 3730 may include, for example, aninfrared communication device, a wireless communication device and/orchipset (such as a Bluetooth® device, an IEEE 802.11 device, a Wi-Fidevice, a WiMax device, cellular communication facilities, etc.), and/orsimilar communication interfaces. Electronic system 3700 may include oneor more antennas 3734 for wireless communication as part of wirelesscommunication subsystem 3730 or as a separate component coupled to anyportion of the system. Depending on desired functionality, wirelesscommunication subsystem 3730 may include separate transceivers tocommunicate with base transceiver stations and other wireless devicesand access points, which may include communicating with different datanetworks and/or network types, such as wireless wide-area networks(WWANs), wireless local area networks (WLANs), or wireless personal areanetworks (WPANs). A WWAN may be, for example, a WiMax (IEEE 802.16)network. A WLAN may be, for example, an IEEE 802.11x network. A WPAN maybe, for example, a Bluetooth network, an IEEE 802.15×, or some othertypes of network. The techniques described herein may also be used forany combination of WWAN, WLAN, and/or WPAN. Wireless communicationssubsystem 3730 may permit data to be exchanged with a network, othercomputer systems, and/or any other devices described herein. Wirelesscommunication subsystem 3730 may include a means for transmitting orreceiving data, such as identifiers of HMD devices, position data, ageographic map, a heat map, photos, or videos, using antenna(s) 3734 andwireless link(s) 3732. Wireless communication subsystem 3730,processor(s) 3710, and memory 3720 may together comprise at least a partof one or more of a means for performing some functions disclosedherein.

Embodiments of electronic system 3700 may also include one or moresensors 3790. Sensor(s) 3790 may include, for example, an image sensor,an accelerometer, a pressure sensor, a temperature sensor, a proximitysensor, a magnetometer, a gyroscope, an inertial sensor (e.g., a modulethat combines an accelerometer and a gyroscope), an ambient lightsensor, or any other similar module operable to provide sensory outputand/or receive sensory input, such as a depth sensor or a positionsensor. For example, in some implementations, sensor(s) 3790 may includeone or more inertial measurement units (IMUs) and/or one or moreposition sensors. An IMU may generate calibration data indicating anestimated position of the HMD device relative to an initial position ofthe HMD device, based on measurement signals received from one or moreof the position sensors. A position sensor may generate one or moremeasurement signals in response to motion of the HMD device. Examples ofthe position sensors may include, but are not limited to, one or moreaccelerometers, one or more gyroscopes, one or more magnetometers,another suitable type of sensor that detects motion, a type of sensorused for error correction of the IMU, or any combination thereof. Theposition sensors may be located external to the IMU, internal to theIMU, or any combination thereof. At least some sensors may use astructured light pattern for sensing.

Electronic system 3700 may include a display module 3760. Display module3760 may be a near-eye display, and may graphically present information,such as images, videos, and various instructions, from electronic system3700 to a user. Such information may be derived from one or moreapplication modules 3722-3724, virtual reality engine 3726, one or moreother hardware modules 3780, a combination thereof, or any othersuitable means for resolving graphical content for the user (e.g., byoperating system 3725). Display module 3760 may use LCD technology, LEDtechnology (including, for example, OLED, ILED, μ-LED, AMOLED, TOLED,etc.), light emitting polymer display (LPD) technology, or some otherdisplay technology.

Electronic system 3700 may include a user input/output module 3770. Userinput/output module 3770 may allow a user to send action requests toelectronic system 3700. An action request may be a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.User input/output module 3770 may include one or more input devices.Example input devices may include a touchscreen, a touch pad,microphone(s), button(s), dial(s), switch(es), a keyboard, a mouse, agame controller, or any other suitable device for receiving actionrequests and communicating the received action requests to electronicsystem 3700. In some embodiments, user input/output module 3770 mayprovide haptic feedback to the user in accordance with instructionsreceived from electronic system 3700. For example, the haptic feedbackmay be provided when an action request is received or has beenperformed.

Electronic system 3700 may include a camera 3750 that may be used totake photos or videos of a user, for example, for tracking the user'seye position. Camera 3750 may also be used to take photos or videos ofthe environment, for example, for VR, AR, or MR applications. Camera3750 may include, for example, a complementary metal-oxide-semiconductor(CMOS) image sensor with a few millions or tens of millions of pixels.In some implementations, camera 3750 may include two or more camerasthat may be used to capture 3-D images.

In some embodiments, electronic system 3700 may include a plurality ofother hardware modules 3780. Each of other hardware modules 3780 may bea physical module within electronic system 3700. While each of otherhardware modules 3780 may be permanently configured as a structure, someof other hardware modules 3780 may be temporarily configured to performspecific functions or temporarily activated. Examples of other hardwaremodules 3780 may include, for example, an audio output and/or inputmodule (e.g., a microphone or speaker), a near field communication (NFC)module, a rechargeable battery, a battery management system, awired/wireless battery charging system, etc. In some embodiments, one ormore functions of other hardware modules 3780 may be implemented insoftware.

In some embodiments, memory 3720 of electronic system 3700 may alsostore a virtual reality engine 3726. Virtual reality engine 3726 mayexecute applications within electronic system 3700 and receive positioninformation, acceleration information, velocity information, predictedfuture positions, or any combination thereof of the HMD device from thevarious sensors. In some embodiments, the information received byvirtual reality engine 3726 may be used for producing a signal (e.g.,display instructions) to display module 3760. For example, if thereceived information indicates that the user has looked to the left,virtual reality engine 3726 may generate content for the HMD device thatmirrors the user's movement in a virtual environment. Additionally,virtual reality engine 3726 may perform an action within an applicationin response to an action request received from user input/output module3770 and provide feedback to the user. The provided feedback may bevisual, audible, or haptic feedback. In some implementations,processor(s) 3710 may include one or more GPUs that may execute virtualreality engine 3726.

In various implementations, the above-described hardware and modules maybe implemented on a single device or on multiple devices that cancommunicate with one another using wired or wireless connections. Forexample, in some implementations, some components or modules, such asGPUs, virtual reality engine 3726, and applications (e.g., trackingapplication), may be implemented on a console separate from thehead-mounted display device. In some implementations, one console may beconnected to or support more than one HMD.

In alternative configurations, different and/or additional componentsmay be included in electronic system 3700. Similarly, functionality ofone or more of the components can be distributed among the components ina manner different from the manner described above. For example, in someembodiments, electronic system 3700 may be modified to include othersystem environments, such as an AR system environment and/or an MRenvironment.

The methods, systems, and devices discussed above are examples. Variousembodiments may omit, substitute, or add various procedures orcomponents as appropriate. For instance, in alternative configurations,the methods described may be performed in an order different from thatdescribed, and/or various stages may be added, omitted, and/or combined.Also, features described with respect to certain embodiments may becombined in various other embodiments. Different aspects and elements ofthe embodiments may be combined in a similar manner. Also, technologyevolves and, thus, many of the elements are examples that do not limitthe scope of the disclosure to those specific examples.

Specific details are given in the description to provide a thoroughunderstanding of the embodiments. However, embodiments may be practicedwithout these specific details. For example, well-known circuits,processes, systems, structures, and techniques have been shown withoutunnecessary detail in order to avoid obscuring the embodiments. Thisdescription provides example embodiments only, and is not intended tolimit the scope, applicability, or configuration of the invention.Rather, the preceding description of the embodiments will provide thoseskilled in the art with an enabling description for implementing variousembodiments. Various changes may be made in the function and arrangementof elements without departing from the spirit and scope of the presentdisclosure.

Also, some embodiments were described as processes depicted as flowdiagrams or block diagrams. Although each may describe the operations asa sequential process, many of the operations may be performed inparallel or concurrently. In addition, the order of the operations maybe rearranged. A process may have additional steps not included in thefigure. Furthermore, embodiments of the methods may be implemented byhardware, software, firmware, middleware, microcode, hardwaredescription languages, or any combination thereof. When implemented insoftware, firmware, middleware, or microcode, the program code or codesegments to perform the associated tasks may be stored in acomputer-readable medium such as a storage medium. Processors mayperform the associated tasks.

It will be apparent to those skilled in the art that substantialvariations may be made in accordance with specific requirements. Forexample, customized or special-purpose hardware might also be used,and/or particular elements might be implemented in hardware, software(including portable software, such as applets, etc.), or both. Further,connection to other computing devices such as network input/outputdevices may be employed.

With reference to the appended figures, components that can includememory can include non-transitory machine-readable media. The term“machine-readable medium” and “computer-readable medium” may refer toany storage medium that participates in providing data that causes amachine to operate in a specific fashion. In embodiments providedhereinabove, various machine-readable media might be involved inproviding instructions/code to processing units and/or other device(s)for execution. Additionally or alternatively, the machine-readable mediamight be used to store and/or carry such instructions/code. In manyimplementations, a computer-readable medium is a physical and/ortangible storage medium. Such a medium may take many forms, including,but not limited to, non-volatile media, volatile media, and transmissionmedia. Common forms of computer-readable media include, for example,magnetic and/or optical media such as compact disk (CD) or digitalversatile disk (DVD), punch cards, paper tape, any other physical mediumwith patterns of holes, a RAM, a programmable read-only memory (PROM),an erasable programmable read-only memory (EPROM), a FLASH-EPROM, anyother memory chip or cartridge, a carrier wave as described hereinafter,or any other medium from which a computer can read instructions and/orcode. A computer program product may include code and/ormachine-executable instructions that may represent a procedure, afunction, a subprogram, a program, a routine, an application (App), asubroutine, a module, a software package, a class, or any combination ofinstructions, data structures, or program statements.

Those of skill in the art will appreciate that information and signalsused to communicate the messages described herein may be representedusing any of a variety of different technologies and techniques. Forexample, data, instructions, commands, information, signals, bits,symbols, and chips that may be referenced throughout the abovedescription may be represented by voltages, currents, electromagneticwaves, magnetic fields or particles, optical fields or particles, or anycombination thereof.

Terms, “and” and “or” as used herein, may include a variety of meaningsthat are also expected to depend at least in part upon the context inwhich such terms are used. Typically, “or” if used to associate a list,such as A, B, or C, is intended to mean A, B, and C, here used in theinclusive sense, as well as A, B, or C, here used in the exclusivesense. In addition, the term “one or more” as used herein may be used todescribe any feature, structure, or characteristic in the singular ormay be used to describe some combination of features, structures, orcharacteristics. However, it should be noted that this is merely anillustrative example and claimed subject matter is not limited to thisexample. Furthermore, the term “at least one of” if used to associate alist, such as A, B, or C, can be interpreted to mean any combination ofA, B, and/or C, such as A, AB, AC, BC, AA, ABC, AAB, AABBCCC, etc.

Further, while certain embodiments have been described using aparticular combination of hardware and software, it should be recognizedthat other combinations of hardware and software are also possible.Certain embodiments may be implemented only in hardware, or only insoftware, or using combinations thereof. In one example, software may beimplemented with a computer program product containing computer programcode or instructions executable by one or more processors for performingany or all of the steps, operations, or processes described in thisdisclosure, where the computer program may be stored on a non-transitorycomputer readable medium. The various processes described herein can beimplemented on the same processor or different processors in anycombination.

Where devices, systems, components or modules are described as beingconfigured to perform certain operations or functions, suchconfiguration can be accomplished, for example, by designing electroniccircuits to perform the operation, by programming programmableelectronic circuits (such as microprocessors) to perform the operationsuch as by executing computer instructions or code, or processors orcores programmed to execute code or instructions stored on anon-transitory memory medium, or any combination thereof. Processes cancommunicate using a variety of techniques, including, but not limitedto, conventional techniques for inter-process communications, anddifferent pairs of processes may use different techniques, or the samepair of processes may use different techniques at different times.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that additions, subtractions, deletions, and other modificationsand changes may be made thereunto without departing from the broaderspirit and scope as set forth in the claims. Thus, although specificembodiments have been described, these are not intended to be limiting.Various modifications and equivalents are within the scope of thefollowing claims.

What is claimed is:
 1. A method comprising: aligning first contacts of afirst component with second contacts of a second component, wherein thefirst component comprises a semiconductor layer stack including ann-side semiconductor layer, an active light emitting layer, and a p-sidesemiconductor layer, and wherein the second component comprises asubstrate that has a different thermal expansion coefficient than thesemiconductor layer stack; performing hybrid bonding of the firstcomponent to the second component, the hybrid bonding comprising:performing dielectric bonding of a first dielectric material of thefirst component with a second dielectric material of the secondcomponent, and subsequently performing metal bonding of the firstcontacts with the second contacts through annealing; and prior toperforming the metal bonding, using chemical mechanical polishing todish the first contacts, the second contacts, or both the first contactsand the second contacts, such that the first contacts are separated fromthe second contacts by gaps when the first contacts are aligned with thesecond contacts; wherein a run-out between the first contacts and thesecond contacts is compensated through closing the gaps as a result ofexpansion of the first contacts and the second contacts during theannealing.
 2. The method of claim 1, wherein: the first componentfurther comprises a second substrate and a buffer layer, the bufferlayer is located between the n-side semiconductor layer and the secondsubstrate, the first dielectric material forms a dielectric layer thatincludes a first side nearer to the p-side semiconductor layer and asecond side nearer to the n-side semiconductor layer, and the firstcontacts are located on the first side of the dielectric layer.
 3. Themethod of claim 1, wherein the chemical mechanical polishing isperformed prior to the dielectric bonding.
 4. The method of claim 1,wherein the first contacts are dished without dishing the secondcontacts.
 5. The method of claim 1, wherein the second contacts aredished without dishing the first contacts.
 6. The method of claim 1,wherein both the first contacts and the second contacts are dished.